Except as otherwise provided in this Agreement, this Agreement shall not be varied, altered, modified, canceled, changed, or in any way amended except by mutual agreement of the parties in a written instrument executed by the parties hereto or their legal representatives, provided however, that the consent of the Employer shall only be given with the prior approval of the Committee and no person acting on behalf of the Employer, or purporting to do so, shall have any authority to do so without such prior approval.