Colo. Rev. Stat. § 37-26-119
Any district intending to issue bonds pursuant to this article may revise, reduce, or cancel classifications of land, assessments, or assessments of or for benefits in substantially the same manner as provided by the laws existing at the time of the original classification or assessments; but no parcel of land shall ever be liable for the payment of an amount greater than the amount for which the land was liable under its original classification or assessment, and the total assessments levied shall not be less than the principal amount of refunding bonds to be issued. Thereafter the qualified voters of the district may vote refunding bonds based upon such reclassification or reassessment of or for benefits. Refunding bonds so authorized may be exchanged on a compromise basis for outstanding bonds and unpaid matured interest thereon, with such owners thereof as may be willing to make such exchange. The rate of interest on such refunding bonds shall not exceed the rate on the bonds refunded, and in no event shall such rate exceed six percent per annum. Refunding bonds issued in accordance with this section shall be secured only by their proportionate share of such new classifications or assessments, and that fact shall be set forth on the face of each refunding bond issued.
C.R.S. § 37-26-119