N.H. Rev. Stat. § 29:11-a
Whenever it shall appear or be made to appear to the commissioner of revenue administration on or before January 1 of any even numbered year that conditions in any town have so changed since the last apportionment of public taxes that the use of the most recently available apportionment would impose an undue hardship upon such town greater than it should in equity and good conscience be required to bear, the commissioner of revenue administration may make such changes and modifications therein as to him seems fair, equitable and just, and certify the same to the treasurer of the county in which the town is situated, and the treasurer shall use such changed equalized valuation in issuing his warrant to the selectmen of such town for such town's just proportion of all taxes granted by the county convention.
RSA 29:11-a
1965, 15:1. 1973, 544:8, eff. Sept. 1, 1973.