Make sure to enable mods if you're unsure watch the video on the nexusmods Front page.
Simply extract the Texture folder into your Data folder, So it looks like Data->Textures->Weapons->Handmade->PipeRifle->Pipegunpalette_d.dds
If it asks to merge folders, Then click Yes.
To Uninstall, Simply remove the Pipegunpalette_d.dds file.
Update. Added the wood "receiver" portion
Update 2. I may continue this line of weapons if anyone asks for it but this was requested by Ninjico
Update 3. Added a "rusted" looking version by request.
Update 4. Added a picture of the palette to show what most texture modders are working with.