I succeeded to start Knoppix with Openbox-LXDE window manager instead of Metacity. I wanted this because I am not satisfied with Compiz, nor Metacity. Bugs, high resource-usage, they does not support the effective work. But Openbox-LXDE is very fast, highly customizable, lightweight and just works. In one word: it is wonderful!
How I achieved this:
First, you have to appply "nocompiz" and "kopik_ncwm" cheatcodes.
Then edit /etc/X11/Xsession.d/45knoppix file.
# kopik.m: use openbox-lxde instead of metacity with "kopik_ncwm" cheatcode
case "$CMDLINE" in *\ kopik_ncwm*) kopik_ncwm=openbox-lxde;; esac
for LXDECONFIG in "$HOME/.config/lxsession/LXDE/config" "$HOME/.config/lxsession/LXDE/desktop.conf"; do
 [ -r "$LXDECONFIG" ] || continue
 if [ -n "$COMPIZ" ]; then
  if grep -q -v '^window_manager *= *compiz' "$LXDECONFIG" 2>/dev/null; then
   # CAUTION: lxsession no longer supports commandline optione for window_manager!
   sed -i -e 's|^window_manager *=.*|window_manager=compiz|g' "$LXDECONFIG"
  if grep -q '^window_manager *= *compiz' "$LXDECONFIG" 2>/dev/null; then 
    sed -i -e 's|^window_manager *= *compiz.*|window_manager='"$kopik_ncwm"'|g' "$LXDECONFIG"
As you can see, one still can use Metacity by not applying "kopik_ncwm" boot option.

Unfortunately, nothing is perfect: now there is an annoying problem: if Knoppix starts with Openbox-LXDE window manager, the notifications are invisible: maybe with black fonts in a very dark background. So, they are totally unreadable. But if I apply "-t 0" option, the text is still visible.
$ notify-send test -t 0
The bug is like described in the following page:
Notification message colour unreadable with "GNOME Classic" session
So, the problem is related somehow to the Openbox-LXDE session, but I do not understand how. Anyone has idea how to resolve this issue?