somewhat similar experience
Just did the same thing in TPE today. I asked the check in agent if I could take an earlier flight, and after a call to the supervisor, got it approved.
I was in Premium Laurel, and on a *A partner's reward ticket number, but I was grateful for their willingness to help out. Will fly BR as often as I can because of this (and past encounters).
Now, the only other thing I have to mention is that it was for TPE-HKG, so obviously more seats and flights from which to choose. You have nothing to lose by trying, though. Good luck!