A good point to ponder, Tom.
True, that one may add sugar, or chaptalise, if the intended final product is apple wine. The rule against doing so, if one intends to distill it into eau-de-vie and label it as apple brandy, is because the final distillate would be a combination of brandy and rum, since sugar was added. There is still a way to bottle this product, as in "spirit of apple cider" but you would not be permitted to call it brandy. Isn't Calvados a great example for making fine apple brandy? No chaptalisation, no hydration, no acidulation and a minimum of three years in the barrel.
All the best,
Rusty