The mortgagee shall make appropriate adjustments in the amount of the requested assistance payments to reflect changes in family income reported in any required or optional recertification of the homeowner or cooperative member. The adjustment shall not be retroactive except at the discretion of the Secretary. The adjustment shall apply only to assistance payments beginning with the payment due no earlier than the first day of the month following and no later than the first day of the second month following the date the mortgagor's recertification is received by the mortgagee.