This Agreement may be amended or modified only by a written agreement executed and delivered by duly authorized officers of Buyer and the Seller Representative (on behalf of the Sellers) (subject to Section 11.7 and Section 11.9(d) , which in the circumstances described therein would require one or more Sellers to sign). This Agreement may not be modified or amended except as provided in the immediately preceding sentence and any purported amendment by any Party or Parties effected in a manner which does not comply with this Section 8.3 shall be void.