Trying to swap weapon models

Somehow I can get the nude mod to work by hiding the original clothing .upk file by renaming it, and then renaming the _BRDF_Mappings.upk version to the original .upk file name.

That said, I want to simply swap weapon appearances. I want my Tommy gun (Colby 1922) to look like the CAP40, I want my Colby RSA to look like the Colby Commander, and I want the OBIR to look like the FFA. Can someone please help me with this? I feel like it should be as simple as swapping the .upk names but when I do that, it makes the affected guns simply disappear, and it also completely wrecks the coloring of every single other gun in the game, changing them to be colored yellow and pink.

Is there something I'm missing? Or what's the problem? Any help with this would be super awesome

Edit: I also posted this somewhere else, and got a response -- "there's a lot of stuff serverside so even if you could do it clientside nobody else would see it so it would be totally pointless" Wrong. I want it to be ONLY clientside so ONLY I can see it. I don't care what anyone else sees. I just want the weapon appearance for myself.