Interesting idea. I think if it were implimented, it would bring up a warning saying you will not score or progress to the next mission if you go ahead with the speed change.
But war games are meant to be strategic and well thought out. Because of the limited control system, you can't hand out orders fast enough, even if you can work them out on the fly.
Perhaps let them slow down the game with no penalty, except in hard mode where it's completely disabled? The game should be accessable by a wide audience, not just experieced gamers.
