I would personally experiment with different designs you want to try. Perhaps the board will break, but then you can tell what you can and can't do. If you were to try something like adding recurves to a board, though, i would do this early in the process, and leave the wood very generous... you will be lucky if a splinter does not lift, but it won't be a problem if the board is thick enough. A good way to bend thick wood is to steam it extensively, and bend it in multiple steps. Adding 4" recurves the first try will definitely not go over well.