I don't think so.
Because isn't the halo application thinking there's only one map and it won't find it.
Just like pasting a new map inside of halo you can't
But then Halo ce fixed that
Ya I think the whole point of the demo or trial w/e you wanna call it is that you can only do a limated amount so you'll buy the full version. But it's likely that someone will hack it or do something to put new maps in.
I was thinking about this earlier. If someone can send you the maps from the purchased game, maybe if you replaced the bitmaps.map, sounds.map, and ui.map, you could rename the other maps as bloodgulch.map or b30.map, and play all of them. It would be tricking them into thinking you