All powers and duties conferred or imposed [F1by or under this Act] shall be deemed to be in addition to, and not in derogation of, any other powers and duties conferred or imposed by Act, law or custom ; and, subject to any repeal effected by, or other express provision of, this Act, all such other powers and duties may be exercised, and shall be performed, in the same manner as if this Act had not been passed.