I've been playing with some of the weapon mods on the workshop. One in particular is JasonBob45's AA12 mod: https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=101349060

I like using this mod because it makes the shotgun not completely worthless later on in the game versus hundereds of enemies at once. However, this mod completely replaces the normal pump-action shotgun, meaning the early levels of a typical campaign are a complete cakewalk. I'd expect the pump-action shotgun to exist for the early levels, then upgrade to the automatic shotgun later on.

It seems that most, if not all, of the weapon mods on the workshop overwrite slots for vanilla weapons. Is this a limitation with Serious Editor 3.5, or is it simply easier to overwrite a weapon? Is it possible to add a new weapon that takes up an unused slot (like the space below the pistol or the rocket launcher)?