The corporation is authorized to pay to the lender, on behalf of a student borrower and out of the corporation's state interest subsidy and loan discount fund, interest accruing on a loan guaranteed by the corporation which is not eligible for payment of the federal interest subsidy provided for in the federal act; provided, however, that no loan shall be guaranteed and no such interest shall be paid by the corporation, unless the loan is eligible for federal reinsurance and federal special allowance payments pursuant to the federal act and unless the state has appropriated funds for use by the corporation for the purposes of this Code section, and that such appropriated funds plus funds then in and projected to become available to the corporation's state interest subsidy and loan discount fund are deemed to be sufficient to enable the corporation to meet its state interest subsidy and loan discount payment obligations to become due and payable during the period of any fiscal year for which the General Assembly has already enacted an appropriations Act. Interest accruing and payable on a nonfederally subsidized loan guaranteed pursuant to this Code section shall thereafter be payable by the corporation at the same times, in the same manner, and during the same periods of time as the federal interest subsidy is otherwise payable on federally subsidized loans pursuant to the federal act. Interest paid on behalf of a student borrower under this Code section is declared to be a loan to the student by the state under this part and guaranteed by the corporation as to repayment by the student in the same manner as if such nonfederally subsidized interest had been deferred and capitalized by the lender holding the underlying loan. The loan of interest made on behalf of a student borrower under this Code section must be repaid by the student borrower by virtue of this Code section and pursuant to provisions set forth in the promissory note executed by the student evidencing the underlying loan. Such interest loan may be repaid by the student, without interest accruing thereon, at any time before maturity of the underlying loan, but shall in any event be repayable in full, without interest thereon, upon maturity of the underlying loan or thereafter, without interest thereon, in monthly installments agreed to by the corporation. Interest loans repaid to the corporation pursuant to this Code section and the underlying promissory note shall be credited to the corporation's state interest subsidy and loan discount fund for further use by the state for purposes of that fund as provided for in subsequent appropriations Acts of the General Assembly. Failure by a student to repay an interest loan owed to the state under this Code section when due shall constitute a default thereon, subject to any forbearance granted to the student by the corporation on behalf of the state, and may thereafter be paid as a default at any time by the corporation; but any default by a student in the payment of an interest loan shall not constitute a default by the student to the lender on the underlying loan. The right of the corporation to collect an interest loan due and owing by a student to the state under this Code section is not subrogated to the right of the lender to collect the underlying loan nor to the right of the corporation to collect any amount becoming due to the corporation on the underlying loan.