Mo. Rev. Stat. § 72.402

The commission shall enact and adopt all rules, regulations and procedures that are reasonably necessary to achieve the objectives of sections 72.400 to 72.423 no sooner than twenty-seven calendar days after notifying all municipalities and the county of the proposed rule, regulation or procedure enactment or change. Notice may be given by ordinary mail or by publishing in at least one newspaper of general circulation qualified to publish legal notices. No new or amended rule, regulation or procedure shall apply retroactively to any boundary change or unincorporated area proposal pending before the commission.