Welcome to the Pit, Razor47 :wave:

Razor47

Now, for the attachments.
You definitely can duct tape a laser pointer or strap a bipod to a FN-FAL but optics would be trickier as it doesn't have any rails at all (in it's basic model anyway). [...] Basic optics like 2x and reflex could easily be ghetto-fit on weapons but more sophisticated ones need at least an original rail to be used through an adapter for precision or for sturdiness on weapons with more kick.

No need for 'Ghetto Style'. There are adapters to put (nearly) every attachment on (nearly) every gun. You can attach bipods and lasers with simple clamps to the barrel. Basic 1.13 and most of it's mods (although UC1.13 to a lesser degree) simply assume attachments to come with all necessary adapters for the sake of simplicity, save for some high tech rail mounted stuff that only fits modern guns.

Razor47

Of course this is all just my rambling as i don't have a single idea how EGC actually works and if you can modify it so deeply or if enemy squads even have a class of their own (quick response, patrol, guard, etc).

Answer to both is 'NO'. EGC can be looked up here
In fact, they don't even know wether they are attacking or defending a sector (one of the big problems with AI).

Razor47

Also i should definitely ask AIM or 1.13 respectable mod crews why aren't night optics still implemented.

There's a night vision scope in AIM, I think it has similar attributes to the ACOG but is quite rare.