The problem is a common property balcony which can be used for BBQs etc which has a locked access door to prevent anyone other than the unit owners or renters from using it, having one of the unit owners keep getting the lock changed by a locksmith so that only he has a key and so is the only one that can use that area.
This must be a common problem. How to prevent one unit owner from getting a locksmith to lock everyone else out. Not feasible in a big city to notify all the locksmiths that they aren't allowed to change the lock without management permission.
The only thing I can think of is to have that notification engraved on the door so that any locksmith can see that but but even then there is nothing to stop the rogue unit owner from gluing a cover plate over that. Surely there must be an elegant solution to what must be a common problem.
Maybe a fancy electronic lock that needs to be unlocked using a phone, but it's a block of 60 units and it might well be a big ask to expect everyone to have a phone capable of unlocking it. And presumably the best locksmiths can just bypass that anyway.