a. A beneficiary shall be permitted to change an optional selection as provided in subdivisions b and c of this section.
b. A change of optional selection may be made by a twenty-year pension plan retiree having a deferred payability date pursuant to paragraph d of subdivision four of section 13-545 of this chapter (relating to change of conditional elections by such retirees) and subdivision c of section 13-558 of this chapter (relating to change of elections by such retirees).
c. If the survivor beneficiary nominated under option two, three or four of section 13-558 of this chapter is a spouse of the retired member, and such person by causes other than death ceases to be his or her spouse or is separated from him or her, or if such option was selected in contemplation of marriage which has not taken place, then the board of estimate shall have authority to permit the change of the optional benefit to the maximum benefit that is the actuarial equivalent by and with the consent of all parties.