I have been using this modified init script for knoppix-8.6.0 for sometime now,
code: https://github.com/insteps/scripts/t...er/knoppix/860

Currently its being used in usb method, but a similar approach would make
it usable via cdrom-boot too.

One can avoid write of iso to usb to start with customization.
Instead just boot the iso, which will detect drive/usb-drives
and look for eg. a folder knoppix<versionum> and layer union-mount
files like <knoppix><num>.sf4 contained in it OR folder <knoppix><num>.d


Maybe not useful and safe enough to add in a distro, but this modification
helps me to add persistent changes and layer them over, even remove/re-add them later.