(a) The board may permit the purchaser of a prepaid tuition contract for a senior college plan or a private college plan at any time during which the contract is in effect and before the beneficiary graduates from high school to enter into a supplemental contract to prepay the tuition and required fees of the beneficiary for a number of undergraduate credit hours, in addition to the undergraduate credit hours included in the primary contract, equal to the number of credit hours purchased for one year under the primary contract. The additional credit hours must be for the same type of institution as the credit hours purchased under the primary contract.
(b) The contract is subject to § 54.620.