InvGuy:
Changing your ST/LT goals is neither a good nor effective strategy. From the AdCom perspective, you had an entire application season to think about your goals. What has changed?
At the end of the day, the schools don't really care about the your goals. They realize many people are going to go in a different direction once they are admitted and there's nothing they can do about it (not that they necessarily care.) The idea is that the goals essays are an opportunity for you to show the school you can put together a well thought out plan for your career and communicate it with conviction. Changing your goals post-decision may communicate confusion and hesitation.
Worse, changing your goals can come off as a cheap "ploy." Anyone can do it without having to put in much energy or effort. It's not like another update where you had to retake a test, earn recognition or launch an initiative - moves that required some level of commitment or achievement. Those are more meaningful updates that could affect someone's standing on the waitlist. Changing your goals will have virtually no impact. If you want to submit an update to improve your standing make it a work status/change, an extracurricular achievement, a letter of reference or (if relevant) a new test score. Good luck!