What Wintersong said, also I think there has been someone who confirmed they were able to 'upgrade' (as in the old one was cancelled so they can do the Elite Founder Pre-order). So I don't think you will have much of a problem and they will be happy to help.
From a business perspective, why wouldn't you let your customer buy the more expensive package after the initial fact. The: "no you got to buy it again and keep the other one," is definitely not a smart business move as it would deny the larger sale most of the time. Stardock, from what I saw, are no fools. 
