In case of a vacancy in the office of commissioner or of any director, the respective deputy shall have all of the powers and perform all of the duties thereof until a successor, either as an acting or regular incumbent, has been appointed and has qualified; provided, no deputy commissioner serving as commissioner in the event of a vacancy shall have power to discharge a director or to revise or change the assignments of activities among the divisions of the department or to designate another deputy. While serving in such vacated office a deputy shall receive the same salary as the regular incumbent.