No, an update cannot be deleted. Roku has the ability to roll back an update, but will only do so under extreme circumstances. There used to be a secret hidden menu that gave a short window for rolling back an update, but I haven't heard of it working for a long time.
No, a factory reset does not revert to an older OS. Whatever OS version it's running when the reset is done remains the OS. A factory reset only clears all of the user personal information and deletes the user account from the device.
The only way to "block" updates is to either power off your Roku when not in use (not just "turn off") or disconnect the network connection. If it's powered and connected to the network, it will check for updates every 24 hours (roughly).
Dan
Roku Community Streaming Expert
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