回複：各位大俠，在下緊急求助，多謝了

Assuming "Prospective Student" is not on original B2:

1) Travel within 30 days only should be OK. The eligibility of return is already given by valid I94.

2) Application for visa will likely be denied, because B2 was changed to F1 without stating "Prospective Student", which is against the original intention of B2. But it's still up to the visa office, if your friend wants to take the risk. But I have to say it's very unsafe to do so.