Mont. Code Ann. § 85-7-1801

The boundaries of any irrigation district organized hereunder may be changed in the manner herein prescribed. Such change of the boundaries of the district shall not impair or affect its organization or its rights in or to property or any of its rights or privileges of whatsoever kind or nature, nor shall it affect, impair, or discharge any contract, obligation, lien, or charge for or upon which it was or might become liable or chargeable had such change of its boundaries not been made.