<p>When I first applied to McGill, I was highly interested in Computer Science, and so applied to the department of Computer Science for the Software Engineering Major. Today, I found out that I've been accepted into the Faculty of Sciences (Yay!)</p>
<p>However, my interests have changed since then - I'd like to change to a Math option and I have noticed that there are some joint Math/CS programs - I'm wondering, how difficult is it to change majors? And would it be easier to change now, when I've just been accepted, or later when I'm actually in the school?</p>
<p>Technically, you haven't picked a major yet as you haven't registered for anything. Since you're accepted in the faculty of science, you could still take, at this point, any science major. Anyway, it's not a problem unless you do it really late (like U2-U3), having done many classes that don't fit into your desired major and not having done all the required courses for that new major in due time. Otherwise, some switches can be done late (e.g. "downgrading" a joint math/cs degree to a math major and cs minor in your last year isn't a problem).</p>