Some interfaces (such as those using Unix-style command lines) may let
you ask for more than one game design when starting up. This is
sometimes useful, for instance, if you want to play on the
steppes
world with a non-standard set of units; your command line
might look like -g my-hacked-standard -g steppes
. You can also
turn things around and load a file with your own changes after a
complete game, as in -g gettysburg -g my-tweaks
.
Be aware, however, that this cannot be guaranteed to work always, since the mixed-together game designs may have mutually conflicting definitions, or interfere with each other in subtle or not-so-subtle ways. Just imagine the disaster if the world consists entirely of terrain that is instant death to your initial units! Worse, Xconq may start up and run OK for awhile, then at the moment you're about to win--the object that you must capture simply cannot be captured by any unit at all.
So be careful about mixing designs!