maybe you misunderstand something. The logic is not to bind a command
to a special shortcut, the other way around is the truth. You can use
several shortcuts for the same command. So, each shortcuts has its
own xfconf property, and you can set your individual configuration in
xfconf without changing the default.
Just try that in one line, maybe in a script for your users:
$ xfconf-query -c xfce4-keyboard-shortcuts
-p "/commands/custom/<Super>l" -t string -n -s xflock4
Date: Sun, 17 Feb 2013 09:30:25 +0100
From: Heiko Adams <heiko.adams(a)gmail.com>
Subject: Change keyboard shortcut for xf4lock
Content-Type: text/plain; charset="utf-8"
by fedora's default the shortcut for xflock4 CTRL+ALT+DEL but I'd
suggest to change that shortcut to SUPER+L because this would be more
intuitive to users which used Windows before. And second CTRL+ALT+DEL
is the shortcut for launching the taskmanager on most systems.