Plutonium

So the other day I was playing Gunji's servers and I saw that they ported weapons over to multiplayer, that got me thinking of how its even possible to make custom weapons, regardless of trying to get the tac shotgun from fortnite into bo2 (because i thought it would be funny to run around with a shotgun from fortnite). Is there any resources I can get to make the custom weapons possible?

Gewehr is there anything i have to do after I check this specific t6 folder in the local app data?