How to customize isolinux.cfg/menu.lst?
> I just want to change/delete some files from /isolinux. E.g. f4.txt
> should be deleted and noted in isolinux.cfg editet. Further It would be
> nice to add/change/delete the boot labels.
You are probably looking for the --templates switch in make-live that indicate
a custom directory, it defaults to /usr/share/live-helper/templates.
Note that if that's only the splash you want to customize you can provide
it through --syslinux-splash switch whitout having the whole tree duplicated.