Can I have a rainbow Gallente Assault?
With a rainbow Duvolle?
And rainbow cat ears?

Sure.

Maybe a bit much with horns and cat ears.
Instead I would say that each module you equip to your suit produces a minor modification that is clearly visible.

So for example.

DMG Mod:
Orange fluid pipes wrapped around firing arm.

Kinetic Catalazyers:
Green fluid pipes wrapped around legs.

Cardia Regulators:
Red fluid pipes wrapped around chest

Prescision Enhancer:
Small Antenna on both shoulders
(Like a geth prime)

Profile Dampener:
All armour plating changes to be more angular

And so on. Then your look is more than just cat ears
(No offence)

These are merely idea but yes the idea is what you fit will determine to small degree your appearance. Since there are so many combinations of modules the combinations will be almost limitless, it would also be mildly useful on the battlefield. Also it is less likely that kt will be abused into stupid versions (look at the creation system on SCV)

And yes I'm aware that's not how scan prescision works, but it doesn't mean a stealth tanked suit can't look like a stealth fighter. It is merely am example to shlw what I meant, you can tweak them, give them multiple version etc. It just seems less immersion breaking than.

Merc, Cat step forward, your assignment is . . . . . . . . . are those cat's ears?
Yeah I'm a Cat, Meow
Right, your assignment is to go home, we don't contract idiots.

(No offence Cat Merc)

Eccentricity is adding a new decal for each tour of duty, or a strike down an arm for each kill. Eccentric is jumping out of a dropship to land on an enemy tankmand plant explosives.

Look at the universe we inhabit, look at all those space faring folk, look at the rich and coloruful back-story built on gritty dark ideals, and you want to introducd cat's ears and pig tails and **** li, that?