Agreed that you can do it, but should you? Keep in mind, you'd probably need to stop by Guest Services (maybe more than once) to prioritize the tickets in your account to make sure they are used as you wish them to be - assuming your tickets are in
MDE and not through some other means. You wouldn't want to waste a park hopper on the one-park day, or have the one-park ticket used and then find out in the afternoon you cannot hop into another park because it used the wrong ticket in the morning.