No employee of the city at the time this charter is adopted shall be required to take any examination in order to continue within the employment of the city. All other provisions of the merit plan will apply to such employees. The incumbents when this charter takes effect who are not elected by popular vote, of all municipal offices not hereby abolished or superseded, shall continue to hold the same until the expiration of their respective terms where a term of years exists, or until such offices are abolished or superseded by lawful ordinances.