This part provides the criteria and procedures for determining and declaring substantial default by a public housing agency (PHA) and the actions available to HUD to address and remedy substantial default by a PHA. Nothing in this part shall limit the discretion of HUD to take any action available under the provisions of section 6(j)(3)(A) of the 1937 Act (42 U.S.C. § 1437d(j)(3)(A)), any applicable annual contributions contract (ACC), or any other law or regulation that may authorize HUD to take actions against a PHA that is in substantial default.