So first thing you is make a folder what ever you want to call it and put it in your server resources. Then inside that folder make a stream folder. Then make a text document and then click on that click save as and click all files and name it __ resource.lua (2X__) Then put all the files for the gun in the stream folder and in the server.cfg put start (what you named your resource)
For a Replacement, it can’t have multiple skins… that would be more on the add on gun skins. With addons you can run the same model multiple times under different names with different features and looks/skins. But I should add all guns, replacement or addons can only have one texture for that specific gun. If you want to change it. You’ll have to change the texture entirely. Hope this helps.