I think an alternate Trooper model with blast visor down would be fine to add some variety to their appearances. Give the visor to heavy weapons and trooper or something along those lines. No extra coding required.

Pro Tip: Not everything in vanilla is possible in mods.

The heavy armor/ light armor should be doable. But as Angel said, visor up/down would replace it. Why don't we make ten kits for the Rebels? Five would be for dudes and five others would be for chicks. They would have the same kits of course.

Vanilla has the option for heavy armour, which drastically alters your appearance.

Short answer: this isn't Vanilla.

..or as Gurd once suggested, a choice between male or female rebel models.

As he's usually medic and therefore the squad chick by default.

That reminds me, those shemales need a voice change.

I don't think it's possible to do more than the custom weapon customization, sadly.

Vanilla has the option for heavy armour, which drastically alters your appearance.
Presumably you could do the same for Rebel Troopers offering them Visor down/up (not neccesarily with any kind of armour benefit) or as Gurd once suggested, a choice between male or female rebel models.

As he's usually medic and therefore the squad chick by default.

It is kind of odd that at the moment the Imperials have more variety than the rebels do in appearance, even though they are supposed to be the ones with the strict uniform, not the rebels.

What I've been considering, though, is a weak, barely noticeable hue covering the screen when flying rebel starfighters, to simulate the orange visor worn by Rebel pilots. Maybe we could also have a breathing sound effect (YT link) when flying an Imperial fighter (though not as intrusive as the one in the video ). Maybe whoever is tasked with coding such a feature could make the pilot breathe faster, a bit more frantically, when the fighter is badly damaged.