What the historical control actually does
The official view model stores the current FastFlag dictionary in memory, then clears the active dictionary when Reset configuration is enabled. Turning it off before committing restores that in-memory copy. The JSON manager saves the resulting dictionary to the managed ClientAppSettings.json location.
That makes the control narrower than deleting a Roblox tree, but the in-memory undo is not a durable backup. Export JSON before reset so the prior state survives saving, closing, or troubleshooting a later write failure.