Wis. Stat. § 800.025

A citation or complaint under s. 800.02 may be amended by the municipality prior to the initial appearance of the defendant. A copy of the amended citation or complaint shall be served personally on the defendant or sent to the defendant by 1st class mail. Otherwise, the citation or complaint may be amended, upon notice and an opportunity to be heard, at the discretion of the court. At trial, the court may amend a citation or complaint to conform to the evidence. If the court amends the citation or complaint to conform to the evidence, the court shall allow both parties an opportunity to present evidence with respect to the amended citation or complaint.