There is some documentation at
http://knoppix.net/wiki/Cheat_Codes#Micro-Remastering
It says both these files need to be edited for 64 bit Knoppix.
/mnt-system/boot/syslinux/syslinux.cfg
/mnt-system/boot/syslinux/syslnx64.cfg
However, I have Knoppix 7.2 DVD installed on a flash drive and, in Knoppix KDE Konqueror, the files are shown as
/media/sdb1/boot/syslinux/syslinux.cfg
/media/sdb1/boot/syslinux/syslnx64.cfg
To see the files I have to first mount the flash drive using the KDE device notifier.