First, a caveat: I haven't tried any of the things that I'm going to suggest. Theoretically, what follows should work, but I make no guarantees.
OK, according to the
manual, you can add a "type" attribute to games in your schedule file that will distinguish between pre-season, regular season, all-star, and exhibition games. Per the manual:
type - The type of game. (0=Regular Season, 1=Exhibition, 2=Spring Training, 3=Playoffs, 4=All-Star Game) For example, type="0" would mean a regular season game. The type attribute is optional, and if it is not included, the game is assumed to be a regular season game.
I've seen a few schedule files that have the all-star game identified, but it's rare, and most schedules don't include game type at all.
So, in the schedule file, you will usually see something like this:
<GAME day="1" time="1905" away="5" home="1" />
To make that a spring-training game, then, you would change it to this:
<GAME day="1" time="1905" away="5" home="1" type="2" />
Of course, if you're making a schedule from scratch, then just add the "type" element to the lines that aren't regular-season games.