So, in my game , the setting is pretty much a war between two gods, and currently, the party (which is a somewhat against both side) finished a big fight on one side. The cleric of the party is a cleric of the other god, so I wanted to have an NPC give him an amulet of the devout to him, thinking the cleric had lost his religious sign since he doesn't know the one of the other god.

Here's the problem, I'm planning to making the items rare, but if he uses it, he lose maybe like XP? Or maybe his spell has a chance to fail like wild magic? I want there to be a consequence to using another gods holy item you know? Then I'm planning of letting him modify the amulet to his god symbol in exchange for lost rarity.

Is this a good idea?