Well I am not a student at MIT yet (start this fall) but my guess is that your best plan for an aero/astro degree from them is to try and get in for not this fall, but fall after that. You need unified engineering as a whole to get the degree, and since unified is a highly specialized course to the MIT curriculum, I doubt you can get credit to place out of it, but I am not really sure. You can't start unified in the 4th term as you need 16.001 and 16.002 (the first half of the year-long unified course) to take 16.003/16.004 (the second half).
I don't think youd be able to graduate with a degree in aero/astro in under 5 years of total undergrad because while you can transfer most GIR credit probably (I am not sure how transfer HASS credit works) I doubt any credit towards the actual degree will be transferable and Aero/astro requires the most units of any major to graduate. Even on the traditional 4-yr degree track it requires a few semesters of 5 classes, so my guess is you'd be looking at graduating with the class of 2013.
Interestingly, if this is actually what happens, you will be in my unified class as I am going for aero/astro and am class of 2013
Again, all this could be completely false, this is what I think is true, I dont know any of this.
Mollie, does Adam know how this works?