N.D. Cent. Code § 49-06-16
The commission from time to time may cause any further hearing and investigation to be had for the purpose of making a revaluation or ascertaining the value of any betterments, improvements, additions, or extensions made by a public utility subsequent to any hearing or investigation, and may examine into all matters which may change, modify, or affect any findings of fact previously made and at such time may make findings of fact supplementary to those theretofore made. Such a hearing shall be had upon the same notice and shall be conducted in the same manner as an original hearing. Any supplementary finding shall have the same force and effect as an original finding, and shall be considered in connection with the original findings and, so far as may be necessary, as a modification thereof.
N.D.C.C. § 49-06-16