Like others have said above, it really depends on the school to which you’re son is applying. He should look closely at that. There seem to be fewer barriers switching majors including to CS or Bus/Econ at many liberal arts schools. For example, I don’t think Bowdoin or Williams had restrictions when we looked at them. MIT also does not pin you down. Obviously Penn, CMU, and UMich are a different story. Internal transfers there, while possible, are difficult.