20(3)Notwithstanding subsection (2), the employer and the bargaining agent or bargaining agents affected may, within 14 days after the day on which the award is rendered, jointly agree, in writing, to amend, alter or vary any provision of an award referred to in subsection (1) and any such amendment, alteration or variation shall be deemed to be a part of the award effective on and after the day on which the agreement to amend, alter or vary the award is signed.