Do you mean you want to keep your data, or do you mean you want to update without using recovery mode?
Whether you use recovery mode or boot to alternate media to do tricks with “dd” you’ll wipe the old data. There is no “live update” in place, the Ubuntu mechanism for live migration will break the system.
You can keep the old system via clone before update. Clones can be loopback mounted on the host…or if the clone is on a hard drive or SD card, then the Jetson itself could loopback mount the clone. The clone would appear like a regular directory tree when mounted in this fashion.