As for other, changing majors within CAS at Cornell is probably no different, or more difficult, than changing majors at any other liberal arts & sciences college. Within the range of majors that the college offers, which are typical of arts & sciences colleges generally. Procedures for changing majors within each of the other colleges probably varies by college.
There are some procedures for double-majoring between majors at different colleges there , but they are likely seldom used, because one must fulfill the different requirements of both colleges. In some cases one can minor in an area taught by a different college.
Switching colleges there requires an internal transfer application process because of the diverse nature of the colleges. There is no a priori guarantee that a random student in the College of Hotel Administration is necessarily up to being able to successfully complete the program at the College of Engineering, or the College of Architecture. For example. There has to be a vetting system to make sure that the transfer makes sense. As long as it does, and the student is qualified, in my experience transfer is not a big deal.
Dartmouth may not need such a formal process since its student body is more homogeneous. Still, if any English major can just switch to Thayer without anybody looking or caring, shame on them. But I doubt that’s actually the case.