This mod lets you customize NPC weapons by replacing the default weapons with any gun from your inventory. This is only a cosmetic choice which will not effect how NPCs use that gun - damage and fire rate of the original gun will be used. Clients will see the default weapons (or whatever they have set up for themselves if they also use the mod). By default it will also add first person weapon firing animations (like pistol slides moving back, revolver chambers spinning, etc) to NPCs and other players (where available).
You can also find this mod on GitHub, so if you want to help with anything, feel free to fork the project, make changes and create a pull request if you're done so I can look at the changes. This is also the preferred way to submit any issues you may have.
Menu is a bit buggy (doesn't close inventory when going back), but can still be used normally