14 CFR 91.817 was changed in the US, sort of, by executive order (depending on if this is legal) and by a proposed bill Supersonic Aviation Modernization Act (SAMA) H.R.3410
I mean, the FAA changes regulations all the time without Congress (when people talk about regulators as a fourth branch of the government, this is what they mean). FAA is under the direction of the Executive Branch.
https://boomsupersonic.com/flyby/breaking-the-sound-barrier-...