The Secretary is authorized to waive compliance with regulations heretofore or hereafter prescribed by him with respect to the interest and maturity of and the terms, conditions, and restrictions under which loans, advances of credit, and purchases may be insured under this section and section
1706a of this title, if in his judgment the enforcement of such regulations would impose an injustice upon an insured institution which has substantially complied with such regulations in good faith and refunded or credited any excess charge made, and where such waiver does not involve an increase of the obligation of the Secretary beyond the obligation which would have been involved if the regulations had been fully complied with.