You're right. This chess game has too many rules. Why can't I add/remove pieces? The board? Why can't I move pieces deeper into or out of the screen? These unspoken rules are imposed on us unfairly. We need to escape the matrix.
There's a way to add and remove pieces now. While dragging, press the SPACE key to clone the piece you're dragging. Press the X key to delete the piece you're dragging.