award, an individual selected to receive a graduate fellowship under this section shall sign an agreement with the Secretary agreeing to pursue a career in instruction at an institution of higher education that has a teacher preparation program in accordance with subparagraph (A). (D) Failure to comply If an individual who receives a graduate fellowship award under this section fails to comply with the agreement signed pursuant to subparagraph (C), the sum of the amounts of any graduate fellowship award received by such recipient shall, upon a determination of such a failure, be treated as a Federal Direct Unsubsidized Stafford Loan under part D of title IV, and shall be subject to repayment, together with interest thereon accruing from the date of the fellowship award, in accordance with terms and conditions specified by the Secretary in regulations under this subpart. (E) Modified service requirement The Secretary may waive or modify the service requirement of this paragraph in accordance with regulations promulgated by the Secretary with respect to the criteria to determine the circumstances under which compliance with such service requirement is inequitable or represents a substantial hardship. The Secretary may waive the service requirement if compliance by the fellowship recipient is determined to be inequitable or represent a substantial hardship— (i) because the individual is permanently and totally disabled at the time of the waiver request