I. If the agreement governing a revolving credit plan so provides, a bank may impose, as interest, a late or delinquency charge upon any outstanding unpaid installment payments or portions thereof under the plan which are in default; provided however, that no more than one such late or delinquency charge may be imposed in respect of any single such installment payment or portion thereof, regardless of the period during which it remains in default; and provided further, however, that for the purpose only of the preceding proviso all payments by the borrower shall be deemed to be applied to satisfaction of installment payments in the order in which they become due. Nothing contained in this section shall limit, restrict or otherwise affect the right of a bank under and pursuant to N.H. Rev. Stat. § 384-G:3 and N.H. Rev. Stat. § 384-G:4 to change the periodic percentage rate or rates of interest applicable to the revolving credit plan between the bank and a borrower upon the occurrence of a delinquency or default or other failure of the borrower to perform in accordance with the terms of the plan.
II. No charges assessed by a bank in accordance with this section shall be deemed void as a penalty or otherwise unenforceable under any statute or the common law.