(a) If a premium is added to the unpaid balance of a retail installment contract under § 345.206 or 345.214, the rate of time price differential agreed to in the retail installment contract remains in effect and shall be applied to the new unpaid balance or the contract may be rescheduled in accordance with § 345.070.
(b) If a premium is added under a retail charge agreement, the premium shall be added to the unpaid balance under the agreement.