- Yes, it is likely that the "other" firmware version is unbootable at this time
- You can revert to stock on either firmware version from the OpenWrt command line, no serial required
- Yes, both OpenWrt and OEM firmware flash the other firmware version when "upgrading"
Reverting to OEM is accomplished by determining which version to overwrite, erasing the NAND, writing the proper firmware image, and, if needed, changing
boot_part. Directions are not provided at this time as I have found that "old" directions tend to be followed blindly in the future, resulting in bricked devices.