Every municipality operating a utility system that includes an electric plant, whether pursuant to this part or any other public or private act or the provisions of the charter of the municipality, county or metropolitan government, that acquires an existing utility system from a municipality, electric cooperative or utility district, has the power and is authorized, but is not obligated, by action of the board or supervisory body having responsibility for such municipality’s utility system, to retain and continue to operate as a separate retirement system any retirement system that was in effect on the date of such acquisition for the employees and retirees of the acquired utility system. Any such municipality shall also have the power and authority to modify, consolidate, amend, open, close and terminate the plans constituting such separate retirement system, and to establish such associated trusts as are necessary and prudent for the proper administration, operation and maintenance of such separate retirement system. Upon the effective date of the acquisition of a utility system in which an election is made to continue the operation of a separate retirement system, as provided for in this section, the assets and liabilities of the separate retirement system shall be transferred to the acquiring municipal utility system and, from and after such date, such assets and liabilities shall be the sole obligation and responsibility of the acquiring municipal utility system and the separate retirement system, but shall not be the obligation of any general retirement system that was in effect for the acquiring municipal utility system prior to the acquisition date. All such assets shall be segregated from the assets of the retirement system of the acquiring utility system and shall be accounted for separately. Such funds may be managed in the same manner as the assets of the retirement system of such acquiring utility system. Nothing in this section shall be construed to impair or diminish the vested rights of any participant in the separate retirement system of the acquired utility system.