Each town clerk may, unless otherwise provided by charter or ordinance, appoint assistant town clerks, who, having taken the oath provided for town clerks, shall, in the absence or inability of the town clerk, have all the powers and perform all the duties of the town clerk. Within ten days after a town clerk appoints an assistant town clerk, the town clerk shall file a notice of such appointment with the Secretary of the State, indicating the name and address of the person appointed, the date and method of such appointment and the law under which the appointment was made. Within ten days after a vacancy occurs in the office of assistant town clerk, the town clerk shall notify the Secretary of the State of such vacancy.