I've gone back and added FMQ lots of times on quilts that have already been bound, no problems!
If this is your very first time doing FMQ, just practice on something prior to putting this quilt under the machine. It's easier than most people think. Just breathe!
When we concentrate, we hold our breath and when we hold our breath, we tense up - not good for FMQ. So put on some music you like and hum or sing along while FMQ to keep yourself breathing and relaxed.