Adding this modification turned out not to be very difficult. 

Next mod for naval Sea Flanker Su-33 only
The Sea Flanker also has a tank refuelling probe in next to the windscreen on the left cockpit side. A small hole was carved in with a file and drill. 

Steps 8 + 9: Next mod for naval Sea Flanker Su-33 only
The wing of the naval Sea Flankers wider in chord and the trailing edge surfaces are different. The rear trailing edge is in fact closer to the horizontal stabilizers and vertical tail. This gives some interesting things to think of (see below).

In addition, the wing may be folded. I decided to go for this interesting folding option also. (You see even parked Sea Flankers with full pylons and "stores" still attached). 

Making the wing larger is best done first now by using thick card for inserting tapered sections at the chords. This is better done at different chord % positions at the upper and lower wing parts A1 & A4 resp. B1 and B4. You get a stronger wing than.

The extended chord is straight tapered and is 1/32 scale  9 mm at the root section and 6 mm at the tip section. This was double checked with the drawings obtained from the internet. 

The wingparts were cut with a razorsaw along the span, the cuts sanded and the tapered plastic card sections made to fit.
Clearly mark all separate parts to avoid confusion!
(Don't bother yet on the separate flaps and slats at this point; the flap and aileron/ flaperon hinge line is the black line in the picture; the red line is only a reference line I used with the drawings).

Another extra change was adding the outboard aileron/flaperon, which is present on the naval Sea Flankers. Always when the wings are folded, the flaperons droop "up" in order to make room for the vertical tails! Look at pictures and you'll see what is needed. 
The flaperons were thus separated from the upper and lower outboard wing sections. 

As the wing would be folded, another chordwise cut was made at the appropriate point for the Su-33 (looking at the scale drawings). The hinge line is outboard and next to the inboard pylon station. 

Similar cuts were made at the tapered plastic insert sections of card.  You have a lot of parts now! Give them a number to avoid confusion. 

Make re-inforcements into the wing parts but do not forget to leave some room in order to add later on a metal folded spar to fix the wing too. Next, all wing parts were glued on flat surfaces and let to dry. 

Some putty and sanding was obviously required. Also, some adjustments to panellines were made, some rivet details inscribed. The basic wings are now ready.

The wings take quite some work, but are a very prominent modifications obviously to get a correct Sea Flanker.

Lets move to the flaps and slats which need a similar treatment, making chordwise cuts. Also the flapsystems are a bit different on the Sea Flanker. Also special is that the Sea Flanker has an extra set of outboard ailerons. I supposed these were fitted for better manoeuvrability needed for safe carrier approaches.

I did not use Trumpeter's solution of rods and metal hinges for the movable surfaces... not needed and it does not really work. 

Please note that the rear inboard trailing edge flaps are double flaps and that they also droop "reverse up" on a parked aircraft. The rib -gaps in the flaps were filled with card and putty and smoothed. Small weight saving holes were also drilled in.

The outboard slats at the canted outboard wing sections are always in a "reverse up" position on parked aircraft and the inboard slats always droop down as there is then no hydraulic pressure.

All in all a very interesting set of wings, flaps and slats.....
Lot of parts, needing carefull assembly and keeping your head straight....

Please note that the drooped trailing edge surfaces were glued and the gaps filled to get a smooth result. Later on, the with a Olfa p-cutter the hinge lines were inscribed.
Also note the aileron. 

Step 11: Fuselage assembly
After fitting the assembled Aires cockpit and wing root sections, the fuselage would be closed. But before that, drill holes in the ribs to accept metal rods later on for added strength. 

Also, (for the Su-33 only) I engraved on the upper surface between the engine fairings 2 extra  grids (I suppose that these are cooling vents). 

After assembly of the fuselage, set aside for lots of drying time. 
I needed some filler at the forward LEX areas, and at the rear next to the stabilizer rotation points.

Note that the larger wing also requires 2 small rear trailing edge sections at the fuselage - wing root area from card. 
The gap still present can be seen in the picture. 

The whole main fuselage assembly was now checked, filled and sanded before the nose was to added.

Step 12
The resin replacement nose of  Zactoman was set onto the front of the fuselage and as small correction were already done as to instructions, this gave no problems. Some filling and sanding was required to get a good end-result. 

NOTES: 
(1) the nose gear bay here is still seen red, which is not correct! It should be light grey.
(2) later on I discovered there should be a small recess / slot between the fairing and nose gear bay. Also the aft fairing on the nose gear door should have a slightly different shape . You may correct this on your kit. 

Step 15+16: fin assembly
These small fins were simply assembled.

 Steps 17+18 and steps with pylons and stores:
Were not yet dealt with, leave for later on. ( Please note however that the missiles in the kit are inaccurate in shape, I will take stores from the Trumpeter Mig-29K naval Flucrum kit in 1/32 scale). 

The maingear-strut fairings parts #28 + d21 are not correct for a Sea Flanker, these fairings are longer than on land based planes. Overall length of a fairing is about 8 cm.

As the Alamo missiles as in the kit are inaccurate anyway, I used the forward nose sections of the missiles parts G3,G4  to make the longer fairings.  A slot was also made. The fairing was blended in with some white glue.

Step 19 Nose gear , mod for naval Sea Flanker Su-33 only: will be covered later on as I need to find 2 right sized wheels (15 mm diameter) as the naval Flanker has a twin wheel nose gear. 

Steps 20-22, mod for naval Sea Flanker Su-33 only
Main gear legs are thicker on naval Flankers to cope with higher loads. I simply twisted Scotch tape around the kit part. Note that I did not use the "springs" supplied in the kit.

 

Pylons

The naval Sea Flankers seem to have slightly different pylons for carrying the "stores" / ordnance. 

The wing pylons top sections are not open but closed. You can use the pylons of the kit with some modification. On the wing pylons, I closed the gaps with some card. The aft section of the pylon on some planes are also a bit simpler; I cut off the rear round stub, but sometimes you see also pylons with the stub (so pick what you want). 

The under fuselage pylons can be used as supplied in the kit, but a small modification is needed at the rear pylon as the tail hook is attached here with a fairing. This as made from some card. (On some Naval Flankers you can also see a very large central pylon for  a very large anti-ship missile). 

The pylons under the intakes on naval Flankers are different as compared
to the kit's pylons. The two stubs of a pylon (parts B9+B10) can be removed and a single fairing made of less height. 

The pylons are also attached a bit inboard under the intake and overlap part of the intake louvres. Pieces a thin card and white glue were used to close the gaps. 

Step 26
The horizontal stabilizers will be mounted a bit angled down and this  requires that the forward sections of the fairings (part #E33+E34) to be removed with a razor saw.

Wing hinges
The naval Flanker have outboard wings sections that can be folded up at an angle to save space on the carrier deck. The hinges were made with card and plastic tube using metal rods to get strength. 

Quite some work is needed as you need to align all the stuff with also the vertical tails and inboard fuselage. 

The outboard winges got a similar "hinge treatment". Pylons were mounted on the outboard wing panels.

Step 38 (with SU-33)
The small fairings in top of the vertical tails are in the other way around on the Sea Flanker; the bigger fairing should be below the small fairing.  A panel was cut out on both fins and reversed.  The vertical fins also needed some little filler at their base to close the gaps.

Step 37
The windscreen and main canopy was obtained from the Zactoman set. The parts supplied are excellent. (see some notes for example the windshield on  Page 1 here.... ).

Some work is needed here as the Zactoman IRTS part can not be used straight away as on the naval Flanker this is not on the center, but right offset. I cut off the IRTS section from the Zactoman part as it would be re-used.

Next, the instrument cover and surrounding areas were painted very dark gray as this would be impossible to reach after the windshield would have been fitted. 

After paint drying, the windscreen was cemented on, and the edges carefully filled with putty. 

The IRTS was put off set and all gaps and the area streamlined with putty. As the clear areas were covered with tape, the gaps below the windscreen were filled in with putty. After 30 minutes drying time, I used nail polish remover to smoothen things up. 
This prevents any damage and works nicely.

First checking of overall fit
Now, the model was to be made ready to receive its first spray coat of light grey to check any flaws. The slats, flaps and pylons were attached to the wings. The inboard slats were also set into position. 

The gear doors, stabilizers and all other small parts were identified and set aside ready for spraying. The detailed cockpit, windscreen insides, and insides of gearbays were masked off with tape and tissue.

Here you see the overall pylon configuration under the fuselage.

After completing a final check up of the overall grey SU-33 and the various sub-assemblies, it was time to add the colour scheme.

Looking at various pictures, you will see many different colourschemes on also the naval Flankers. For the Su-33 a particular plane was picked found on the internet with plenty of "walk around" pictures.

Su-33 "Red 80" has a Tiger on its tail!  It seems that the "normal" Flanker colours were used also on this naval  Flanker with rather sharp demarcation lines between the different colours.

XTRACOLOR has the Flankers enamel colors in their range with X601 medium blue, X602 light blue and X603 blue/grey

Airbrushing takes far less time than the masking, but it is extremely important to take your time here. First, I masked off the cockpit, nose, windscreen and wheel bays. Then came in the airbrush.

Starting with the lighter grey/blue X602, the overall model and the various sub-assemblies were given an overall coat. The trick when spraying XTRACOLOR is to use for thinning a mix of 20% white spirit, 20%  thinner and 60% paint.

After 24 hrs drying time, next was the tideous task of masking off the particular areas on the upper surfaces of the model. I used Revell transparant masking foil and some Tamiya tape in areas. As the picked out Su-33 has a pretty complex scheme, this took quite some time (about 3 hours).

Than the X601 medium blue was sprayed on. After 24 hours, the next and final masking was done, putting on the X603 blue/grey color.

But then you're not ready yet.....

On some areas you will find white antenna panels. And what about all those timy small metallic leading edges on the vertical tails, wings, stabilizer and... canards! Also the engine air intakes need an edge here. 

The engine exhaust area got a mix of Humbrol aluminium "metal coat", Testor metalizer "aluminium" and the exhaust pipes themselves also a coat of Testor metailzer "titanium". Yep, it's all in the masking. 

The inner surfaces of the gear doors got a coat of bright red (not yet seen in the pictures).

Overall it took about four days and 20 "working hours" to apply the colours. The end-result was quite OK I guess, so the work was worth the effort. The Sea Flanker came to life with it's colours on and looks a bit like a lizard with those typical Flanker colours.

The markings for the Russian Navy Su-33 Sea Flanker "Red 80" with the Tiger symbols have to be made with decal as there are no commercial Sea Flanker decals sets in 1/32 scale. 

I used good pictures to copy the patterns in a picture editing program, sized it to the correct dimensions and printed the patterns onto Bare Metal foil  sheets: 1 sheet of CLEAR inktjet decal paper and 1 sheet of White inktjet decal paper.
After printing and drying, the inkts were sealed with Microscale liquid decal film. 

The pattern made you can see here; download for your personal use as you see fit.... vertical height of the rectangle should be 11 cm on 1/32 scale.