Mo. Rev. Stat. § 545.300
An information may be amended either as to form or substance at any time before the jury is sworn, but no such amendment shall be allowed as would operate to charge an offense different from that charged or attempted to be charged in the original information. If an indictment be held to be insufficient either as to form or substance, an information charging the same offense charged or attempted to be charged in such indictment may be substituted therefor at any time before the jury is sworn. No amendment of the information or substitution of an information for an indictment as herein provided shall cause a delay of the trial unless the defendant shall satisfy the court that such amendment or substitution has made it necessary that he have additional time in which to prepare his defense.
§ 545.300, RSMo