Hmm, I would recommend changing UCSD, not USC. Why? Because USC is a rolling admissions school but UCSD is not. When I interviewed last year (3rd session), the acceptance rate was 15% for interviewers. If I had interviewed at the first or second session, the acceptance rate would've been around 50%. Those who interview early have a much higher chance of being accepted.
Sorry to burst the bubble for you late interviewers.