In counties having charters that provide a method of appointment and tenure of office for the superintendent, matron, and other employees of the juvenile hall, the charter provisions shall control as to those matters and, in counties that have established or hereafter establish merit or civil service systems governing the methods of appointment and the tenure of office for the superintendent, matrons, and other employees of the juvenile hall, the provisions of the merit or civil service systems shall control as to those matters. In all other counties, these matters shall be controlled exclusively by the provisions of this code.