update school about compensation after submission

I won't weigh in on the promotion/raise/bonus importance issue, since I frankly don't know it. Some schools are very adamant about not receiving any extra information whatsoever after the submission of your application, whereas other schools will welcome the extra information. You should call the admissions office of each school to ask about that before submitting anything at all, especially since you don't want to appear a nuisance if that is indeed a school that doesn't want anything.

If you do encounter a school that doesn't want extra information, you can and should give updates (even an updated resume if appropriate) during the interview. The interviewers are typically asked to ask about further updates for your application as the schools recognize that a lot can happen in a couple months.