Nobody can say for sure the bitcoins in that address are stolen. But it would be very possible to reject bitcoins from certain addresses, and the protocol don'

Nobody can say for sure the bitcoins in that address are stolen. But it would be very possible to reject bitcoins from certain addresses, and the protocol don't need to be changed. All it would take is make a client to reject to include transactions to/from blacklisted addresses into blockchain. And for everyone to update clients. That still would be vulnerable to 51% attack, but it is very real possibility.