N.H. Rev. Stat. Ann. § 461-A:22

Every agreement made under RSA 461-A:21 shall state whether the agreement either is modifiable or is not modifiable. To qualify as not modifiable, the agreement shall state a specific dollar amount to be contributed by either or both parents. If the parents' agreement states that it is modifiable, the legal test for modification shall be a substantial change in circumstances that was not foreseeable when the agreement was signed.