No elected or appointed Shelby County official or sheriff 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. Every elected or appointed Shelby County official 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, and shall be treated as an employee of the county. Shelby County officials 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. No person may participate in both a supernumerary program and the Employees' Retirement System based on the same service. For the purposes of this amendment, the words "elected or appointed Shelby County official" shall include any person appointed to serve the remaining term of an elected or appointed Shelby County official. The words do not include a judge, county commissioner, district attorney, legislator, constable, school board member, or any official elected from a judicial circuit.