Given that your connection is not less than the minimum connect time, I doubt DL would change you for free, though of course it can't hurt to try. If it helps, my last 6 BOS-LAX flights were 30 minutes early, 10 minutes early, 25 minutes early, 20 minutes early, 10 minutes early, and 5 minutes early, and all arrived into T5. If it were me, I'd try to change off of the 35 minute connection and if DL said no, I'd have a backup plan ready to present to the GA/service desk in case you miss the LAX-SYD flight.