I mean, no, you can't really change the weapon sprites without loading the mod, because of how it works...?
Sorry that there's a breakdown in communication, but I'm not sure what to suggest from here.
Is there any chance you're asking for a way to only have skins, and not the vanilla weapon sprites? If so, there's technically some code you could change (the 8 on line 125 - if you want vanilla skins to never show up change it to a 0), but other than that I don't think I can help you.