Thank you though most of the things i kinda figured already. Sadly it isn't enough to just edit the tgas. At least i didn't see any difference when doing so. And as you said Blender is just pain. I now kinda give up on it.
It's annoying though, i took me 5 Minutes doing it in Rexuiz (that xonotic fork) and an old Version of Xonotic (but then i wouldn't be able to use the new Weapon Models).
It bothers me because i think it would be really nice to have the Pickup Models similar to Quake Champions. I think it's just really nice and looking much cooler than that 2d "simple items". So in case it isn't clear what i wanted to do here is an example. In Quake Champions all weapons have a specific color before getting picked up. So it is a nice way to tell what weapon you gonna pick up without needing simple-items (Which look way wore in my opinion). I just think it would be a nice addition to xonotic, especially when using competitive Settings. So in case someone is able to do what i wanted to do i really would appreciate it. Maybe i should suggest it as an Idea for xonotic? I mean it should be really easy to do for someone who is knowing HOW to do it because as i said it takes like 5 Minutes to accomplish it in old xon.