Is this possible?, how?

[Capricorny]

If you use syslinux boot, you can edit boot/syslinux/syslinux.cfg, and eventually add more alternatives to suit your needs
The stanza for booting the 64-bits kernel in 7.6.1 is

LABEL knoppix64
KERNEL linux64
APPEND lang=en apm=power-off initrd=minirt.gz nomce libata.force=noncq hpsa.hpsa_allow_any=1 loglevel=1

Here you may add another entry, for example if you have KNOPPIX in a directory KNOPPIX761_0 on /dev/sda1 - using knoppi65-0p at the boot prompt:

LABEL knoppix64-0p
KERNEL linux64
APPEND lang=en apm=power-off initrd=minirt.gz fromhd=/dev/sda1 nosound knoppix_dir=KNOPPIX761_0 nomce libata.force=noncq hpsa.hpsa_allow_any=1 loglevel=1

And the same without persistent image

LABEL knoppix64-0
KERNEL linux64
APPEND lang=en apm=power-off initrd=minirt.gz fromhd=/dev/sda1 noimage nosound  knoppix_dir=KNOPPIX761_0 nomce libata.force=noncq hpsa.hpsa_allow_any=1  loglevel=1

I haven't used syslinux for a long time, so there may be some errors here, but you get the idea. I have a version number on the KNOPPIX directories, as there may be several remasterings of a release on the same partition. Furthermore, you may want to patch minirt.gz, for example going over to squashfs instead of cloop. Then you save it under another name, and use that for the initrd boot parameter. Same if you change the kernel.