The commission shall not order changes in the total rates or impose stranded cost, system benefits, or other restructuring charges under N.H. Rev. Stat. Chapter 374-F if the result would be to cause changes in the total rates charged to, or the accounting for revenue received from customers taking service from a rural electric cooperative under special contracts approved pursuant to N.H. Rev. Stat. § 378:18 for the duration of those special contracts in effect as of May 1, 2000.