If you press your wand to your body and imagine yourself with golden hair, afterward your hair will fall out. If you visualize yourself as someone with clearer skin, you will be taking a long stay at St. Mungo’s. And if you Transfigure yourself into an adult bodily form, then, when the Transfiguration wears off, you will die.”
Most likely Transfiguring only your brain or a single organ would fall under partial Transfiguration, which presents the obvious challenge.
Chapter 15: