I made a new .esp that just overrides the MPP for Vivec, the wraithguard, and for the "unique dwemer item" back to vanilla.

But when I kill vivec, he doesn't have the Unique item in his inventory. If I add it to the game world everything works (quest, equip, daedric looking), but I don't want to have to use the console or easily pick it up in order to get a second wraithguard.

Is there a script blocking it? Help pls...

I can't find out how to add anything to vivec's inventory. Including a mod adding his armor to the game. Someone's hadto havedone this before. pls.

drag and drop from the list of items into the npc's inventory box

You could just add it to your inventory with a console command after killing Vivec.