(4) Where by or under any enactment any functions are conferred upon a public officer, the Governor General may direct that, if by reason of absence or incapacity through illness or any other cause that officer is during any period unable to perform those functions, such functions shall be performed by a public officer or person designated by the Governor General, and during any such period the public officer or person so designated shall perform such functions, subject to such conditions, exceptions and qualifications as the Governor General may direct.