Mo. Rev. Stat. § 407.907

An artist who is a consignor may lawfully waive the provisions of subdivision (3) of section 407.904 if such waiver is clear, conspicuous, in writing, and signed by the artist who is the consignor. No waiver shall be valid with respect to the proceeds of a work of fine art initially received "on consignment" but subsequently purchased by the consignee directly or indirectly for his own account. No waiver shall inure to the benefit of the consignor's creditors in any manner which might be inconsistent with the rights under sections 407.900 to 407.910 of the artist who is the consignor.