I asked that question yesterday to an SA (not mine since mine isn't always the easiest to get a hold of). If you find a demo you like, you would have your $100 and, apparently, your RN# get transferred to the demo. You will not be moved back to the line or anything like that. Having said that, there are a few caveats.
(1) There is a decent likelihood that your demo will have some blemishes. If it's major, they'll take care of it. If it's minor, then you have to live with it. The example they gave me for a minor blemish is curb rash on your rims.
(2) You will not get a chance to view the car prior to making the decision. The first time you see the car will be the day you take delivery. If you refuse to accept the car as is, you will then be "moved to the back of the line" so to speak.
Now I don't know how true any of this is. It's almost like I'll get a different answer from different SA's on any given day.