Okla. Stat. tit. 12A, § 12A-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 or other signed record 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be otherwise modified or rescinded, but except as between merchants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.