(1) With respect to a precomputed consumer credit sale or consumer loan, refinancing or consolidation, the parties before or after default may agree in writing to a deferral of all or part of one or more unpaid installments, and the seller or lender may make and collect a deferral charge not exceeding the amount of the sales finance charge or loan finance charge attributable to the first of the deferred monthly installment periods multiplied by number of months in the deferral period (the period in which no payment is required or made by reason of a deferral): Provided, That no installment on which a delinquency charge has been collected or partial payment made shall be deferred unless the amount of the delinquency charge or partial payment is first applied to the deferral charge. If prepayment in full occurs during a deferral period, the portion of the deferral charge attributable to the unexpired full months in the deferral period shall be also rebated.

(2) The seller or lender, in addition to the deferral charge, may make appropriate additional charges, and the amount of these charges which is not paid in cash may be added to the amount deferred for the purpose of calculating the deferral charge.

(3) The parties may agree in writing at the time of a precomputed consumer credit sale or consumer loan, refinancing or consolidation that if an installment is not paid within ten days after its due date as originally scheduled or as deferred, the seller or lender may unilaterally grant a deferral and make charges as provided in this section. No deferral charge may be made for a period after the date on which the seller or lender elects to accelerate the maturity of the agreement.

(4) With respect to a real estate secured consumer credit sale or consumer loan, the parties before or after default may agree in writing to a modification or amendment of, or allonge to, the consumer credit sale or consumer loan, and the seller or lender may make and collect a modification charge equal to the greater of $250 or one percent of the outstanding balance of the consumer credit sale or consumer loan at the time of the modification, amendment or allonge: Provided, That no modification charge may be made where prohibited by federal law or regulation.

(5) The commissioner shall prescribe by rule the method or procedure for the calculation of deferral charges consistent with the other provisions of this chapter where the precomputed consumer credit sale or consumer loan is payable in unequal or irregular installments.