Also some people mistake the SPSPA and subsequent amendments for the law. They aren't. The law is HERA. Nowhere in HERA does it prevent a pay down of the principal.
The SPSPA and amendments were signed by heads of FHFA and Treasury. The current heads of the same agencies can undo the crooked deals their predecessors signed. It wouldn't be breaking any laws. On the contrary, it would be upholding the US Constitution.