upgrade cramfs root file system while running

i have a cramfs image, which is my rootfs(/ partition) on flash. i
found some discussions which say that upgrading it while mounted was
prone to errors. however if i am doing the upgrade only in my
shutdown scripts (so that most applications are killed by this time)
like this:
mount -o loop -t cramfs rootfs.img /tmp/somedir
eraseall /dev/mtd2
cp rootfs.img /dev/mtd2
export PATH=/tmp/somedir/bin:/tmp/somedir/sbin...
export LD_LIBRARY_PATH=/tmp/somedir/lib
reboot
is there anything that could go wrong? All further programs(with their
libs) should be executed from the
loop mounted rootfs.
or else can i do something like
mount -o loop ...
cd /tmp/somedir
pivot_root . tmp
eraseall, copy
reboot
Since i am upgrading just before reboot only these scripts would be
running. Is there a risk in
either/both of these methods.

Thanks
Ganesh