could it be set directly in the registry? if so, we could use tripleX's registryDLL to switch it before the game starts and turn it off again at exit. unfortunately, i only found out how to configure the limits (eg. AA16x) on msdn, not how to set the desired value.
some other game developers give the user a choice where you can switch between anti aliasing and no anit aliasing. I don't think they change settings in the hardware
Heres how antialising works: you have to recreate the main backbuffer surface when you enable or disable multisampling (aniti-aliasing). Not normally a big deal..
