Yeah, that’s how I was originally doing it. The problem is the pieces are unmasked often through the game and the non-owning player would sometimes accidentally select all of them and mask the italian units and thus taking ownership of them.
I was considering making two versions of each italian unit that masks, one which is owned by the German player and one which is owned by the allied player(s). Then put a replace with other trait to swap them out. There aren’t a lot of them so I may see if I this works.