You could do it with chroot but it is not even necessary in this case.
Boot you slack installation disk, then, as advised on the very first screen you will see (before pressing [return] just type exactly this after the boot: prompt
Code:
huge.s root=/dev/sda2 rdinit= ro
and press [Enter]. Your system will then start as usual and you will be able to make the necessary modifications to /etc/lilo.conf then run lilo again.
I assume that /dev/sda2 is your / (root) system partition from your first post.
Don't forget to keep the lilo stanza for the huge kernel this time in addition to the one for the generic kernel. Just in case
PS Andrzej was faster. But again, use /dev/sda2 if that's your root partition.