You cannot just suddenly increase a room occupancy, without a full review with the local Fire Marshal's office allowing to do so. It is not the size of the room or the demand. It is the ability for people to exit properly through the existing structure.
While POR and CBR were able to do so, because their exits are on the exterior and modifications can be made to do so, with an existing interior structure, you cannot suddenly increase the width of the interior corridors for the ability of proper exiting when add "X" number amount of people to each floor. You also have to realize that all of the people above the floors you are located must use the same exiting stairs.
It is virturally impossible to do without major renovations.