Any special act to the contrary notwithstanding, the legislative body of any town having a city or town manager as its chief executive officer, may, by ordinance, permit the chief executive officer to appoint (1) not more than six departmental coordinators to coordinate work of department heads and (2) a deputy city or town manager and assistants to such deputy. A departmental coordinator may be designated as a deputy city or town manager or as an assistant to such deputy. Any coordinator, deputy city or town manager or assistant to such deputy shall serve at the pleasure of the chief executive officer.