What do the schools even signify? Do you get special access to classes? are there different graduation requirements? I’m applying to Humanities as an art major
As far as I know, anyone can take any class as long as they have the prerequisites or signed permission from the professor. There may be exceptions to that, but I’m not aware of any. It does go the other way, though: professors tend to be generous and sometimes promise not to turn away an intended major for the department the class is under if the course is a requirement. Note that I said department, not school (e.g. Computer Science, not Engineering).
The schools are generally a collection of departments with similar or overlapping subject matter and resources. They don’t really represent any kind of barrier for students.