Should it be valid for an app to replace the sound file for a given `soundName`?  For instance, if they had a sound called `backgroundMusic` and they wanted to replace it on every level instead of having `backgroundMusic1`, `backGroundMusic2`, etc?

I agree that it's probably not the *preferred* method, but maybe it should be a warning instead of an error?  Of course, then we actually have to unload the first sound and load the second.