Is it legal to have individual locks (with keys) on a non-bedroom room in a condo?

Dear Asker, you're asking the wrong questions. The real issue here is whether the additional "bedrooms" are an illegal subdivision of the property. If you are the tenant, I suggest that you look up the apartment information on 311's website with the department of buildings to see whether there is a certificate of occupancy for the additional bedrooms. The lookup tool is on the bottom left of the page. This information is also available from the County Clerk Or Registrar of your county. If you are the owner, then consult a real estate attorney about making LEGAL subdivisions to the unit.

Dear New York Tenant: The general rule is no locks on interior rooms in an apartment for any reason. Note: a rented dwelling cannot rent individual rooms legal or not to different tenants. That violates the NYC law prohibiting creating rooming house units within an apartment.

I do not think it illegal to put a lock and key on a door within an apartment when used by a residential tenant or tenants. I can think of situations, such as remote home offices, which would require this for confidentiality or HIPAA related compliance. Taking a room in a rental unit and locking it off for someone other than the tenants' use is another story though. But to say that a lock and key is prohibited in apartments, would mean that no private dwelling space could have a bedroom locked off with a key lock. Even in private homes. That could not possibly be something the law could prohibit.