Mo. Rev. Stat. § 472.130

Any person legally competent may in person or by attorney waive in writing any notice required by this code or by rule or order of court. A personal representative may make waiver either in person or by attorney. A guardian of the estate, conservator, or a guardian ad litem may make a waiver on behalf of his protectee or ward, and a trustee may make a waiver on behalf of the trust. A consul or other representative of a foreign government, whose appearance has been entered as provided by law on behalf of any person residing in a foreign country, may make waiver of notice on behalf of such person. Any person who submits to the jurisdiction of the court in any hearing waives notice thereof.