Sure. I daresay it's even been done a few times, and certainly a fair number of people have played Steve's old campaigns, when he used to distribute them rather than the Tutorial game with database upgrades. THe biggest impediment to doing so at the moment is the inability to turn over control of an NPR to the computer, so while you can set the location, size, and government type of your 'enemy' empire, you can't influence it's ship designs or tech research choices.
