The CD/DVD/USB image(s) built by livecd-creator normally use syslinux
as the bootloader, so you can edit it's config file under /syslinux/syslinux.cfg
(on the disc image).
Obviously you can't edit them once you burn the image to a CD/DVD, so you have to do it before. To do that, you can 'loop' mount it, with something like:
mount -o loop image.iso mount-point