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Describing a Fool is currently impossible, as there is no Betza notation for that. Because the diagram doesn't enforce turn order, the concept of 'previous move' is a bit fuzzy. Although it is used to implement e.p. capture. So I suppose it should not be too difficult to fix this.

As to promotions: when you specify a zone depth of 3 it would ask you to choose a piece from the legend every time you move a Pawn to rank 8, 9 or 10. By specifying a promoChoice that includes P it will also allow non-promotions. But you could then always pick all allowed pieces everywhere. To refuse 'promotion' to P on rank 10, and to N, B and Q on rank 8 and 9, you would have to put additional JavaScript in your submitted page. Before performing any move the diagram tries to call a function WeirdPromotion that it does not define itself, and which must specify the piece to appear on the to-square, as a result of the move coordinates and proposed piece. I use that in Werewolf Chess to force pieces that capture a Werewolf to turn into one:

function WeirdPromotion(x1, y1, x2, y2, promo) {
  if((board[y1][x1] & 15) != 6 && // King immune
     (board[y2][x2] & 15) == 5) promo = board[y1][x1] & 1024 | 5 + 512;
  return promo; // normally a no-op
}

It should be possible to provide code here that would turn a Pawn on 10th rank to Q, and the choice of a Queen into a Rook on 8th and 9th.

Note that the diagram is not (yet) intended as a way to actually play the game. Just as a convenient way to demonstrate how the pieces move.