A person employed in an administrative or supervisory position by more than one district shall be given regular classification in whichever district he or she may select for the regular classification. Other regular classification shall be given to such an employee in a district situated wholly or partly within a city or city and county where the charter of the city or city and county provides for other classification. This section shall apply only to persons whose first day of paid service in the district without a break in service precedes July 1, 1990.