Mont. Code § 2-9-521
Whenever any sureties on the official bond of any officer wish to be discharged from their liability, they and such officer may procure the same to be done if such officer will execute a new bond in accordance with the provisions of this part in like form, penalty, and conditions, and to be approved and filed as the original bond. Upon the filing and approval of the new bond, such first sureties are exonerated from all further liability, but their bond remains in full force as to all liabilities incurred previous to the approval of such new bond. The liability of the principal and surety or sureties in such new bond is in all respects the same and may be enforced in like manner as the liability of the principal and sureties of the original bond.
§ 2-9-521, MCA