The Secretary may make such rules and regulations as may be necessary or desirable to carry out the provisions of this subchapter, including, without limiting the foregoing, rules and regulations relating to the maintenance by the investor of books, records, and accounts with respect to the project and the examination of such books, records, and accounts by representatives of the Secretary; the submission of financial and operating statements and the approval thereof; the submission of claims for payments under insurance contracts, the proof of the validity of such claims, and the payment or disallowance thereof; the increase of the established investment if the investor shall make capital improvements or additions to the proj­ect; the decrease of the established investment if the investor shall sell part of the project; and the reduction of the outstanding investment for the appropriate operating year or operating years pending the restoration of dwelling or nondwelling facilities damaged by fire or other casualty. With respect to any investor which is subject to supervision or regulation by a State banking, insurance, or other State department or agency, the Secretary may, in carrying out any of his supervisory and regulatory functions with respect to projects insured under this subchapter, utilize, contract with, and act through, such department or agency and without regard to .section 6101 of title 41