A. A holder may by agreement with the buyer extend the due date of all or any part of one or more installments under an existing retail installment sale agreement, a refinancing agreement or a consolidation agreement.

1. (1) Shall be in writing and signed by the parties;
2. (2) Shall incorporate by reference the agreement to which the extension agreement applies;
3. (3) Shall state the terms of the extension;
4. (4) May provide for an extension charge not to exceed one per cent of each installment for each month from the date when such installment or part thereof would otherwise have been payable to the date when such installment or part thereof is made payable under the extension agreement; provided, that when any such charge is made, no delinquency charge as provided in section twenty shall be charged unless an installment as extended is not paid by the end of the grace period beyond the extended due date;
5. (5) May provide that the buyer shall pay the additional cost, if any, for insurance coverage provided in the extension; and

6. (6) Shall clearly set forth the fact of any extension charge, the amount extended, the date to which, or the time period for which payment is extended, the amount of the charge for the extension, and the amount for the additional cost of insurance, if any, resulting from the extension.

   C. If the extension agreement extends the due date of only one installment, it need not be in writing but shall be subject to the provisions of clauses (4) and (5) of paragraph B. If no charge is made for the extension agreement, the agreement shall not be subject to paragraph B.

B. Except as provided in paragraph C, an extension agreement