How much will my chances change if I don’t do an interview?
It all depends.
There are some comments you may find helpful, and a specific instruction to do further looking, in this thread:
http://talk.collegeconfidential.com/discussion/comment/20058052#Comment_20058052
if you can interview, then you should. However, if interview isn’t available, then it shouldn’t affect your chances. I didn’t get an interview.
I would recommend doing an interview, as it’s added into considering interest for CMU, and will only help you. If you don’t do it, try to attend other events to demonstrate interest, as that can improve your chances. Don’t worry about it too much though if it would be very hard to arrange an interview.