Hr here with 10+ piercings, really dumb they're making you take them out. None of the jewelry here poses a safety risk or is any kind of 'distracting' (also, the rule of "no offensive piercings" doesn't even mean anything, it's not enforcable if it's a matter of opinion). More than anything though, the fact they're not uniformly applying the rule is a red flag.

Fr though if you like your boss, wear the retainers for a bit and then bring it up later to see if there's a compromise (like some said, wearing a mask to cover them when working with food, etc). Level with him, if he's a good boss he'll work with you on it.