When an optional mode of settlement of National Service Life Insurance or United States Government life insurance heretofore or hereafter matured is available to a beneficiary who is a minor or incompetent, such option may be exercised by such beneficiary’s fiduciary, person qualified under the Act of February 25, 1933 (
25 U.S.C.
14), or person recognized by the Secretary as having custody of the person or the estate of such beneficiary, and the obligation of the United States under the insurance contract shall be fully satisfied by payment of benefits in accordance with the mode of settlement so selected.