This behavior will not be preserved in the client, though you will still be able to change flags in Studio using whatever method you would be using today.
This simply isn’t sustainable and requires that we play cat and mouse and constantly make sure that specific FFlags can’t be abused. Also, even if this was added, it certainly wouldn’t include reverting to old CoreGui, as the end state of most flags is for the code it’s replacing to be completely removed for maintainability reasons–we would just be encouraging delaying the inevitable.