The elected officials' plan and any related trust agreement, investment advisory agreement, custodial agreement, annuity contract, or similar agreement, may be amended by the county at any time, either prospectively or retroactively, to conform to the provisions of the Internal Revenue Code. However, if the Internal Revenue Service requires an amendment and the amendment reduces a benefit provided by the elected officials' plan, the required reduction must be paid as a separate benefit from a nonqualified supplemental plan to be established by the county. The benefit payable to a member from the elected officials' plan and the related benefit payable from the supplemental plan, when taken together, must equal the benefit promised under the elected officials' plan immediately before the benefit amendment required by the Internal Revenue Service. (1987 L.M.C., ch. 27, § 13; 1987 L.M.C., ch. 44, § 4; 1988 L.M.C., ch. 25, § 1.)