(a) Consideration unnecessary for modification.--An agreement modifying a contract within this division needs no consideration to be binding.

(b) Writing excluding modification or rescission.--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signed agreement which excludes modification or rescission except by a signed writing cannot be otherwise modified or rescinded, but except as between merchants such a requirement on a form supplied by the merchant must be separately signed by the other party.

(c) Compliance of modified contract with statute of frauds.--The requirements of section 2201 (relating to formal requirements; statute of frauds) must be satisfied if the contract as modified is within its provisions.

(d) Ineffective modification or rescission as waiver.--Although an attempt at modification or rescission does not satisfy the requirements of subsection (b) or (c) it can operate as a waiver.

(e) Retraction of waiver.--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.