Where this article allocates a risk or a burden as between the parties "unless otherwise agreed", the agreement may not only shift the allocation but may also divide the risk or burden.
Okla. Stat. tit. 12A, § 2-303
Oklahoma Code Comment
There are no previous Oklahoma decisions which have stated this rule, but it is a well recognized principle. See Garrison Coal Co. v. Semple, 82 Okl. 60, 198 P. 497 (1921); E. M. Brash Cigar Co. v. Wilson, 32 Okl. 153, 121 P. 223 (1911).