Right now you have to duplicate the element (or group of elements), then convert to symbol, for there is no way to break it. This is the most useful feature, if you need to create similar symbols.
If you select a Symbol in the Resource Library you can click the duplicate button at the bottom to create a separate version of the Symbol.
Thanks. This helps, but I'd prefer to be able to change a thing or two in the new symbol without having to drag it to the scene, just double click on it in the library.