My coworker made a reservation under a set code for 3 rooms all under his name. I am now joining the trip and wanted to change the reservations into my name since I am Platinum and he is not, and we want to get the upgrade/free breakfast/etc. Unfortunately the price has gone up so I don't want to just book a new reservation. Is this something I should call SPG ahead of time to try and change? Or will I have better luck doing it at the hotel?

I have been able to add someone's name to the reservation on the phone in the past if they are arriving earlier, but they always kept my SPG number / benefits.