In this case, it wasn't Muhammed who said, "oh, sorry, I have changed my mind." It was the judge who said, "nope, you're not going to represent yourself anymore."
But, isn't that the same kind of instance? I mean, could a judge do that in the case of a trial by jury....suddenly decide that the juy's not doing it's job & decide to render the verdict himself?
In both cases it would be going against the legal wishes of the accused.