The commission may, from time to time, cause further hearings and investigations to be had for the purpose of making revaluations or ascertaining the value of any additions, betterments, extensions, and new construction made by any public utility subsequent to any prior hearing or investigation, and may examine into all matters which may change, modify, or affect any finding of fact previously made, and may at such time make findings of fact supplementary to those theretofore made. Such hearings shall be had upon the same notice, and be conducted in the same manner, and the findings so made shall have the same force and effect as is provided in this chapter for original notice, hearing, and findings. Findings made at such supplemental hearings or investigations shall be considered in connection with and as a part of the original findings, except insofar as such supplemental findings change or modify the findings made at the original hearing or investigation.