This is my cousin's problem. In the first week of March he was offered a PhD offer (Upper Middle ranked School in USA) in Physics and he received his I-20 to get the visa.The admit was fully funded. He accepted the offer because he didn't have any offer at that time. But few days ago, a top ranked school admin said to him that, he might be admitted as a lot of students haven't accepted their offer (it is not guaranteed though plus admission is completed ).
He was always expecting to get admitted in that school. The deadline of the offer letter from first school is 15th April (He accepted the offer already).
Will it be possible to decline the first offer later/admission if he gets the offer after around two weeks from the top ranked school? I want to know the consequences of this situation.
I have received another suggestion from academia. He suggested to defer the admission (if he gets from the second university) from the Top ranked school. After a semester completed in the first admitted University, If my cousin feels that he should change the department, he will be able to do it. How reasonable is this?