No elected or appointed Revenue Commissioner in Montgomery County may assume a supernumerary office after the effective date of this amendment. Any person who, on the effective date of this amendment, is entitled to participate in a supernumerary program may continue to participate in that supernumerary program, which shall include the assumption of a supernumerary office according to the terms and conditions of the law which established that supernumerary program. The Revenue Commissioner of Montgomery County may participate in the Employees' Retirement System of Alabama upon the same terms and conditions as may be specified by law for any other employee in the same retirement system. The Montgomery County Revenue Commissioner holding office at the time of the ratification of this amendment shall be eligible to purchase service credit in the Employees' Retirement System for the time the official has served in the current office; provided, however, the official shall forego the assumption of a supernumerary office. This amendment does not include a county commissioner, a judge, district attorney, legislator, school board member, or any official elected from a judicial circuit.