The regulations in this subpart may be amended by the Commissioner at any time and from time to time, in whole or in part, but such amendment shall not adversely affect the interests of a mortgagee or lender under the contract of insurance on any mortgage or loan already insured and shall not adversely affect the interests of a mortgagee or lender on any mortgage or loan to be insured on which the Commissioner has made a commitment to insure.
24 C.F.R. § 207.499