Most likely you will not be able to switch. Last year I tried to get into a different session and they literally didn't have a chair for me and I was denied. It was frustrating but hey, that's why you sign up in advance. You can only switch if someone else switches out or if there is still room in the session. Fire codes and space and all that.
I also think the authors are paid a percentage of how many people sign up for their workshops (I don't know this but I do suspect it). It's a separate fee so it makes sense.
Pick one and stick with it my friend.
