Any member of the plan who is retired and who has selected a survivor option may cancel the survivor allowance payable to his or her designated beneficiary. Such election shall be in accordance with the rules and regulations prescribed by the Board of Control and once made by the member shall be irrevocable. Any member who so elects to cancel a survivor allowance shall designate such new beneficiary as he or she shall nominate to receive a pro rata payment for the number of days the member shall live during the month of his or her death. Any cancellation of a survivor allowance under the provisions of this section shall be irrevocable by the member and payment of the pro rata amount for the number of days the member lives during the month of his or her death shall be in lieu of any other benefits heretofore payable.