Their reservations explained page sounds like you can change it when your ordering window opens up. Doesn't say there are limitations on which model, 4 door vs 2 door, etc.
I don't have an official letter saying it is, but from my contacts the answer is yes. However, I can also seeing Ford saying no since the demand is high.
This is what is super annoying. You should be able to preorder and not worry about the prices announced be marked up. What's the point of a reservation. Whether you like Tesla or not, I like their no nonsense the price is the price and your position in line is when you will get to exercise...