Sorry for late response...
TFTP will not work on LAN for me, and I would like to reverse engineer the firmware (just like I did with the script that is proven to work) to see if I can make it work, but I only have one device and I’m using it for production (it’s my NAS for Time Machine).
As for the procedure in both my script and it’s inspiration, the Linksys OEM update script, boot sector is not touched at all.
The only thing that is done is to enable the autorecovery feature (not needed in OpenWrt as it’s always enabled) and to switch the boot partition to the one which is not booted. It uses the default uboot-env-tools available in OpenWrt.
An extra step made by my script is wiping the “syscfg” partition, where the OEM firmware stores it’s settings. Nothing else is done.
But, as far as I understand (did not test), TFTP should be usable on LAN (Linksys even provided the tools). More research is needed, but as long as the device is not hard bricked, the BackToStock method should always work.
Any bug reports are welcome, but you should use the Issues feature on my repository on GitHub to grab my attention regarding to the prebuilt, the scripts and it’s documentation.