The kernel is being written into it's own partition. The script does not reformat your root filesystem, but does copy the modules onto the root filesystem.
flash_eraseall -j /dev/$Mtd
nandwrite -pm /dev/$Mtd sheeva-$KVer-uImage
Please, be more specific in your answer. If I run the commands above in my plug without changing anything in my system, which will be the result, a bricked plug or an updated kernel plug?
Thanks for your patience!