(a) If the unpaid balance of a retail installment contract is extended, renewed, restated, or rescheduled under this subchapter and § 353.114 does not apply, the holder may collect an amount computed on the principal balance of the amended contract for the term of the amended contract at the time price differential for a retail installment contract that is applicable after reclassifying the commercial vehicle by its model year at the time of the amendment.
(b) The principal balance of the amended contract is computed by:
(1) adding:
(A) the unpaid balance as of the date of amendment;
(B) the cost of any insurance incidental to the amendment;
(C) the amount of each additional necessary official fee; and
(D) the amount of each accrued delinquency or collection charge; and
(2) if the time price differential was computed using the precomputed earnings method or the scheduled installment earnings method, subtracting from the total computed under Subdivision (1) an amount equal to the prepayment refund credit required by § 353.120 or 353.121, as applicable.

(c) Subsection (b)(2) does not apply to a retail installment contract in which the time price differential is computed using the true daily earnings method.
(d) The provisions of this chapter relating to acquisition costs under the refund schedule under § 353.120 do not apply in computing the principal balance of the amended contract.