Question: How odd would it look for someone to switch into an AP at semester? Do you think I'd be treated as less than just taking it full year?
I don't think it would look at all odd to switch into an AP in the middle of the school year. It could, in fact, be a small plus because it will suggest to college admission officials that you were eager to challenge yourself more than you were being challenged in the first semester. So as long as you feel that you can catch up with your classmates who have been there since September and won't be overwhelmed, then there's really no down side.