I know that for the most part anytime you are out of combat you can change your skills on your bar, and you can change the chosen 10/20/30 point traits for your build. But to change the actual trait point allocation, you have to buy books from the vendor to refund your trait points as far as I can see.
My questions is can you somehow have a separate "build" for Dungeons and/or WvWvW and/or PvP? So when you go into those zones you can change freely? Or every time I jump to WvWvW or want to do a dungeon I have to go buy the books and respec everything? I could never find a way to do that in the BWEs, but then again, I only got to level 13, so didn't get much time to explore a lot of random things.