In the event of divorce of a member who retires under an optional retirement plan, where the spouse is the designated beneficiary, the beneficiary may be cancelled upon the written request of the member and proper documentation, which shall include the final decree and marital dissolution agreement of the parties; provided, that such cancellation is not in conflict with the decree or marital dissolution agreement. The retirement allowance payable to the retiree after the cancellation of the designated beneficiary shall not be affected by such cancellation.