Of course, I need to do some work in between... hence, the question.
To unpack, I can use 'unmkinitramfs'.
But, I can't seem to repack an initrd from current directory. 'mkinitramfs' always takes stuffs from my system directory (/lib/modules/x.y.z/). Current directory has many add-ons from the original initrd, that I don't have, so I don't want to lose it.
mkinitramfs -v -r ./ -o ~/new_initrd.img x.y.z
According to manpage, "-r ./" should force the root directory as current directory, but it doesn't seem to.