Wis. Stat. § 971.29: Amending the charge.

(1) A complaint or information may be amended at any time prior to arraignment without leave of the court.

(2) At the trial, the court may allow amendment of the complaint, indictment or information to conform to the proof where such amendment is not prejudicial to the defendant. After verdict the pleading shall be deemed amended to conform to the proof if no objection to the relevance of the evidence was timely raised upon the trial.

(3) Upon allowing an amendment to the complaint or indictment or information, the court may direct other amendments thereby rendered necessary and may proceed with or postpone the trial.