(a) By notice signed by the veteran or his duly authorized agent, and delivered or properly mailed to the Department of Veterans Affairs during the lifetime of the veteran. Such change shall not take effect until approved by the Secretary and after such approval the change shall be deemed to have been made as of the date the veteran signed said written notice and change, whether the veteran be living at the time of said approval or not.

(b) Or by last will and testament of the veteran, duly probated. Such change shall not be effective until received by the Department of Veterans Affairs and approved by the Secretary and after such approval the change shall be deemed to have been made as of the date of death of the veteran: Provided, That a change of beneficiary signed subsequent to the date upon which the will was executed and delivered in accordance with paragraph (a) of this section shall if approved in accordance with regulations take precedence over the designation by will.