It's entirely doable, some years ago I went a bit further relayouted partition altogether on Kindle 2 - so as to prevent the system partition taking up space (poor thing was like 2GB, and fw root few hundreds mb of space used...). File sync then rigged with mtpd (usb) & samba (wifi).
As a method to block OTA it's overkill, as you're already editing initrd to begin with, and you can do far simpler things there to block OTA.
|