Wis. Stat. § 806.32: Variation by agreement.

(1) The parties may agree to vary from the effects of ss. 806.30 to 806.44 at any time before or after the commencement of an action or distribution proceeding, or the entry of judgment.

(2) The parties may agree upon the money to be used in a transaction giving rise to a foreign-money claim and may use different moneys for different aspects of the transaction. Stating the price in a foreign money for a particular transaction does not require, of itself, the use of that money for other aspects of the transaction.