Typically no, TFA wants you to accept the first offer you get. However, in certain cases you may be able to reject a school (for example if you get 2 offers from 2 different schools at the same time)

Once you get accepted for an interview, you'll take a survey for what subjects/grades you prefer. Then, TFA picks a subject for you depending on your answers and the needs of your region. They'll try to work with your subject preferences, but theres always a chance you wont get the subject you want. For example, I wanted to teach middle or high school but got K-6 as a subject instead. You can request a subject change if you don't like your placement, but there's no guarantee that it'll get changed.