(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) 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.