Amends the Internal Revenue Code to permit certain amendments, waivers, or other modifications to mortgages held by a Real Estate Mortgage Investment Conduit (REMIC) or a Grantor Trust without disqualifying such mortgages as REMIC or Grantor Trust mortgages. Permits amendments, waivers, or modifications that do not: (1) extend the final maturity date of a mortgage; (2) increase the outstanding balance of the mortgage; (3) result in the release of an interest in real property securing the mortgage; or (4) result in an instrument or property right which is not debt for Federal income tax purposes. Exempts such amendments, waivers, or modifications from the penalty for prohibited transactions.