Mo. Rev. Stat. § 448.1-104: Variation by agreement.

Except as expressly provided in sections 448.1-101 to 448.4-120, no provision of sections 448.1-101 to 448.4-120 may be varied by agreement, and no rights conferred by sections 448.1-101 to 448.4-120 may be waived. No declarant may act under a power of attorney, nor use any other device, to evade the limitations or prohibitions of sections 448.1-101 to 448.4-120 or the declaration.