85-7-2031. Amending or supplementing United States contracts -- effect on indebtedness. The board of commissioners of any irrigation district established and organized under and by virtue of the laws of Montana, whenever deemed advisable and to the interests of the district, shall have the power and authority to enter into any contract with the United States supplementing or amending any original contract with the United States, said original contract having been entered into pursuant to the provisions of 85-7-1906 and 85-7-2012 through 85-7-2018; provided, that such supplementary or amendatory contract does not increase the amount of the principal indebtedness of the district to the United States as it exists at the date of the supplementary or amendatory contract authorized under the provisions of 85-7-2012 through 85-7-2015.