As for your chances… I suggest looking thru this valuable thread:
I do not recommend emailing or pestering your admissions rep “a lot” as you suggest. If you ever do need to genuinely communicate with USC Admissions, you can express your interest in and demonstrated commitment to USC… but you do not really need to say it more than once. A big factor will be how your essay(s) and written answers within the Common Application convey that fact… i.e. have you researched USC? Why USC? etc.
I would list a true second major. They can also always admit you “Undeclared” if those two major programs initially pass on you. So, I would not list Undeclared as Option 2.
Good Luck…