Amendments not to render invalid notifications, orders, etc., issued before commencement of this Act

3. The provisions of this Act which amend the Code, or any other Central Acts, or the State Acts specified in the second Schedule, so as to alter the manner in which, the authority or the law under which or in accordance with which, any powers are exercisable shall not render invalid any notification, order, commitment, [before the commencement of this Act; and any such notification, order, commitment], attachment, bye-law, rule or regulation or thing may be revoked, varied of undone in the like manner and to the like extent, and in the like circumstances, as if it had been done after the commencement of this Act by the competent authority and in accordance with the provisions then applicable to such a case.