There's nothing that we can do about this. I have to talk to several people and see if it is possible to blacklist certain parts from showing up. Right now, the game picks whatever parts is available with no regards to any sort of rule.

I really hope that this can be fixed, or at least circumvented. A small side of me thinks that it might an engine level problem, which can't be fixed without the source code of the engine.

Another idea would be to make the armor an actual armor as a side to each tier, disallowing any soldiers from getting the armor parts unless they equip the armor. An idea worth considering.

I think putting it as being useable by Veteran's only might help to circumvent that. If not that, then meh.

Unless OP is referring to them getting put into use as soon as you change the Armor that someone has equipped, as I doubt anything can be done there except for maybe using the Uniforms-Manager-Mod to circumvent having to manually change every piece of armor again, which is what I do.

I'll have to try the Uniforms Manager