Monte os squashfs:
mkdir /mnt/squishy
mount mfs.sqash /mnt/squishy -t squashfs -o loop
Copie os squashfs para outro lugar:
mkdir /tmp/squooshtacular
find /mnt/squishy -xdev -print0 | cpio -pa0V /tmp/squooshtacular
Copie os novos arquivos para o lugar:
cp ./a.foo /tmp/squooshtacular/a.foo
Crie os novos squashfs:
mksquashfs /tmp/squooshtacular mfs_with_bbq_sauce.squash