A friend of mine takes estrogen and has breasts, feminine voice, etc. Her body’s arguably taken both sexual differentiation pathways over the years. I think even this definition isn’t so clear-cut.

Body modification through technology doesn’t really encroach on the scientific classification of the natural world. The Vacanti mouse which had an apparent human ear grown on its back was an amazing thing in its own right, but its existence doesn’t mean we need to update our understanding of what a mouse is.