Notwithstanding any provision of this part, a retired member who was a Member of the Senate or Assembly may revoke an optional settlement and may designate a different beneficiary by a writing filed with the board. The new beneficiary shall receive an allowance based upon the actuarial equivalent, as of the date of the election, of the retired member’s allowance payable for the remainder of the lifetime of the retired member under one of the optional settlements specified in this article.