Mo. Rev. Stat. § 247.310
No petition with the requisite signatures shall be declared null and void on account of alleged defects, but the court may at any time permit the petition to be amended to conform with the facts by correcting any errors in the description of the territory, or in any other particular, except that the boundaries of the district may not be enlarged by taking in additional territory, without notice to the voters thus affected, which notice may be made by publication or service of such pleadings and orders. Similar petitions or duplicate copies of the same petition for the organization of the same district, revising the boundaries of the proposed districts, or recommending another chosen name for the district or recommending other voters for the first board of directors, or recommending a different maximum rate of levy for general operating purposes may be filed at any time before a hearing is had on the petition, and shall, together with the first petition, be regarded as one petition, and shall be considered by the court the same as though filed with the first petition placed on file.
§ 247.310, RSMo