Mo. Rev. Stat. § 400.9-603: Agreement on standards concerning rights and duties.

(a) The parties may determine by agreement the standards measuring the fulfillment of the rights of a debtor or obligor and the duties of a secured party under a rule stated in section 400.9-602 if the standards are not manifestly unreasonable.

(b) Subsection (a) does not apply to the duty under section 400.9-609 to refrain from breaching the peace.