Mont. Code Ann. § 7-31-105

In the event it shall be found expedient and proper in executing said contract to modify or change the same in some of the minute details thereof and such modifications or changes shall be agreed upon by the parties thereto, the same may be made with the approval of the judge or judges of the district forming such county or the judge or judges of the district in which such county or incorporated city or town is included and, when so approved, shall have the same force and effect as if originally contained therein.