If a group of tenants and the landlord all sign a "joint and several" lease for a house or multibedroom apartment, nobody can make changes until that lease agreement expires (at least not without the agreement of everyone on the lease).
If it's an SRO lease where they are leasing just a single room and access to common areas then yes the landlord can lease rooms as he can find tenants for them.
If it's an SRO lease where they are leasing just a single room and access to common areas then yes the landlord can lease rooms as he can find tenants for them.