Section 23A. A town may by vote or by-law authorize and empower the selectmen to appoint an executive secretary or town administrator who may be appointed by them for a term of one or three years and to remove him at their discretion. An executive secretary or town administrator appointed under the provisions of this section shall be sworn to the faithful performance of his duties. During the time that he holds office he shall hold no elective town office, but he may be appointed by the selectmen or, with their approval, by any other town officer, board, committee or commission, to any other town office or position consistent with his office. He shall receive such aggregate compensation, not exceeding the amount appropriated therefor, as the selectmen may determine. He shall act by and for the selectmen in any matter which they may assign to him relating to the administration of the affairs of the town or of any town office or department under their supervision and control, or, with the approval of the selectmen, may perform such other duties as may be requested of him by any other town officer, board, committee or commission.