As a followup to the good responses you've received, you might try to work out a compromise with your board. If you can limit your stay-alone guests to one family (for example), you might find that the board is willing to make an exception. "My sister Mayella and her husband would like to stay in the apartment for two weeks every summer" is much more appetizing than "Random friends of my choice will be living here in my absence whenever I feel like it."

Also, don't try to argue that you shouldn't be bound by a new House Rule you didn't expect. That argument is going to lose. See Horwitz v. 1025 Fifth Avenue, in which a new House Rule required a shareholder to remove an awning that had been in place for *decades*. But again, if your Proprietary Lease contains the unusual provision that guests may stay in your absence, then there's a good chance a House Rule wouldn't be able to override it. A lawyer would need to address that question.