Mo. Rev. Stat. § 545.290

The statute of jeofails, as applicable to criminal pleadings and proceedings in prosecutions by indictment, shall apply to all proceedings in prosecutions by information; and any affidavit or information may be amended in matter of form or substance at any time by leave of court before the trial, and on the trial as to all matters of form and variance, at the discretion of the court, when the same can be done without prejudice to the substantial rights of the defendant, on the merits, and no amendment shall cause any delay of the trial, except at the instance of the defendant for good cause shown by affidavit.