Exactly-WashU is pretty flexible in that regard. Students do not actually declare their major until 2nd semester sophomore year.
There is also a lot of cross-pollination so to speak with kids with majors/minors in different divisions. My son has a CompSci minor in Engineering as well as his primary major in Arts and Sciences-and he has a double major in History to go with the Biology major. He knew somebody in his freshman dorm who was a double major in History and Computer Science.
There are students who have switched from Engineering to Olin Business as well.