OPINION — AG — QUESTION: " CAN A RETIRED TEACHER, AFTER SELECTING HIS PLAN OR RETIREMENT AND RECEIVING PAYMENTS UNDER THE PLAN SELECTED, CHANGE TO ANOTHER OPTION? " — NEGATIVE CITE: 70 O.S. 1961, 17-5 [70-17-5], 70 O.S. 1961, 17-6(7) [70-17-6], 70 O.S. 1961, 17-5(2) [70-17-5] (W. J. MONROE)