All administrative powers, duties, and functions of the city shall be vested in the City Manager, except as otherwise provided in this charter. He shall be appointed by the Commission on the basis of training and ability in the work which would qualify him for the position of City Manager, and shall hold office at the pleasure of the Commission. He need not be a resident of the city at the time of his appointment but shall, unless excused by the Commission, become a resident of the City within ninety (90) days after his appointment and so remain throughout his tenure of office. The City Manager, may, with the approval of the Commission designate an administrative officer or employee of the city to perform the duties of the City Manager during his temporary absence or incapacity. The Commission shall designate a qualified person to perform the duties of City Manager during a vacancy in the office. No person acting as City Manager in a temporary capacity, whether during the absence or disability of the City Manager or during a vacancy in that office, shall make any change in the administrative officers of the City without the consent of the Commission. No person who holds or has held any elective city office shall be eligible for appointment as City Manager or acting City Manager, nor shall any such person perform the duties of the City Manager during a vacancy in that office until two (2) years have elapsed following the expiration of the term for which he was elected.