Section 2--209. Modification, Rescission and Waiver

(1)  An  agreement  modifying  a contract within this Article needs no
  consideration to be binding.
    (2) A signed  agreement  which  excludes  modification  or  rescission
  except  by  a  signed writing cannot be otherwise modified or rescinded,
  but except as between merchants such a requirement on a form supplied by
  the merchant must be separately signed by the other party.
    (3) The requirements of the statute of frauds section of this  Article
  (Section 2--201) must be satisfied if the contract as modified is within
  its provisions.
    (4) Although an attempt at modification or rescission does not satisfy
  the requirements of subsection (2) or (3) it can operate as a waiver.
    (5)  A  party  who has made a waiver affecting an executory portion of
  the contract may retract the waiver by reasonable notification  received
  by  the other party that strict performance will be required of any term
  waived, unless the retraction would be unjust  in  view  of  a  material
  change of position in reliance on the waiver.