Using mount --bind, you can point a different file for that file. I think this makes the job well. But needed to mounted at every boot up. You can do it by Advanced script.
Other approach is updating the /dev/bml0/6 partition. For doing that,
*you needed to dump your root image
*move that image to your PC
*modify it via SquashFS/FAT image
*and flash your flash chip.
*pray to god.( Always needed specially while doing critical things)
I haven't try unmount root partition before. I don't know what happens. First try it.

AFAIK, TV's firmware update process doesn't unmount that device before flashing.
You needed to stop watchdog before. And you have to know that If you make a mistake in new/modified firmware, than your TV could be bricked. It's probably could recoverable. But It's better to have all partitions image as a backup.
If I were you, I will
*Revert firmware to previous one
*download last firmware of TV from Samsung,
*put modified root image dump as "rootfs.img" to the /image directory, near exe.img.enc on new FW that gonna flash.
*update validinfo.txt file and add requied changes that described at bottom
*than flash it as usual firmware update.
*pray to god.( Again, not forget )
This will safely flash "rootfs.img"
You could needed to update validinfo.txt file too.
Its structure is basic, for example:
Code: Select all
*007_exe.img_35bda3e4*011_appdata.img_69153622
Your new valid.txt needed to be like:
Code: Select all
*006_rootfs.img_1234abcd*007_exe.img_35bda3e4*011_appdata.img_69153622