From my experience last year, I do believe they are reserved. If you go to the Stabletop Game area, there should be a sheet of paper to sign up.
I'm not sure of everyone else's games, but my game "Dungeons & Dragons: Enter Equestria" would allow basically any race. I have a sheet of a few of my self-made races for the game, though I can come up with other races on the fly.
If you have any other questions, feel free to ask! Hope to see you there!