Wis. Stat. § 214.505: Modification agreements.

Except as provided in a loan contract, a savings bank may enter into a written agreement with a borrower to modify the terms of a loan that describe the amount, time or method of the payments, the interest rate or any other provision of the loan contract. The loan contract, security instrument and lien priority are not affected by the modification, even if the modification was not provided for in the loan contract, unless the modification increases the total amount to be loaned under the loan contract.