FROM: https://unix.stackexchange.com/questions/80305/mounting-a-squashfs-filesystem-in-read-write
As root, copy filesystem.squashfs to some empty dir, e.g.:
cp /mnt/clonezilla/live/filesystem.squashfs /path/to/workdir
cd /path/to/workdir
Unpack the file then move it somewhere else (so you still have it as a backup):