"Buyer's remorse" is not unheard-of. One of my PS roomies really really wanted USAFA and the Air Force, and another guy in my plebe year company really wanted USMA. They both graduated and commissioned in the USN. One five-and-dived, one retired after 20 years in service.
As 845something described, it's damn near impossible to leave one academy and gain appointment to another, so really: best put that out of your mind as an option. Try to identify which jobs most interest you, and then see about pursuing those MOSs through USMA. Please please please also keep in mind that you are very, very early in your process of becoming an officer. You have four years of education and training yet to come! It is quite likely that you will change your interest at least once. There is research on how often college freshmen change majors, and it is a very high frequency: north of 75%, or 3 out of 4. Since people are pretty much the same everywhere, and develop in a lot of the same ways everywhere, it cannot be that different for service academy plebes/doolies/swabs. Even those plebes who have done their homework, so to speak, really have no idea what the all the different opportunities are, and what warfare communities are like (what their goals, culture, workdays, perks etc. are). Frankly, you also have so much to discover about yourself: the strengths and weaknesses you already know about, and those yet to be discovered. You will find your fit.
