for the manual repackaging, you use simg2img to convert the file into a proper img, then mount the img file, copy the tarball from the mount into a temporary dir and use make_ext4fs from the package to create one using this temporary dir as input for an image of the appropriate size.
for the manual repackaging, you use simg2img to convert the file into a proper img, then mount the img file, copy the tarball from the mount into a temporary dir and use make_ext4fs from the package to create one using this temporary dir as input for an image of the appropriate size.