No elected or appointed sheriff in Montgomery County may assume a supernumerary office after the effective date of this amendment except as provided herein. 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 Sheriff 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 sheriff 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.