24 C.F.R. § 242.43
Application of cost savings
At the sole discretion of HUD, any cost savings shall be used to:
(a) Reduce the principal amount of the mortgage and the mortgagor's cash equity contribution proportionally, unless the mortgagor elects to have a greater portion of the savings used to reduce the mortgage; and/or
(b) Fund any additional construction or substantial rehabilitation approved by HUD.