Question about Admission into a major at MIT

Hi everyone,
I was exploring MIT’s website and there were a couple of things that were unclear to me. After you get accepted to the university, how do you get admitted into a school? Do you have to be admitted into a school at time of undergrad admissions to get a particular degree (e.g. do you have to be admitted into the School of Engineering at time of undergrad application to be able to pursue the CS Engineering degree)? Or do you get into a school during your sophomore year at MIT? Also, is CS/CS-interdisciplinary degree a capped major at MIT? If so, how does MIT decide who gets to choose what degree?

(P.S. Can somebody from MIT help me understand how easy it is to change majors? I know you go into MIT undeclared if you get accepted, and right now I’m planning to study CS+Molecular Bio if I get into MIT, but will I be able to choose a different major than the one I expressed interest for on my undergrad application if I happen to change my mind?)

MIT doesn’t admit by major. You can declare a major at the end of your first year, or wait until the end of your second year.
https://mitadmissions.org/help/faq/majors/
http://catalog.mit.edu/mit/undergraduate-education/academic-programs/majors/
https://mitadmissions.org/discover/the-mit-education/majors-minors/

Right, but does MIT limit how many people can pursue a particular major? Are there any caps, and if so, how does MIT do it?

In general, there is no limit to how many people can choose a particular major.
As I recall, the only exceptions to this were if you wanted to pursue a Sloan school-based major, such as management.
Otherwise, you are pretty much free to pick whatever major you want.

no