ChessVariant: Special rules for promotion doesn't seem to make very much sense in this game, since the pieces change with every move anyway. A pawn on the 7th rank would have gotten there by accident, because you never hoped for it to become a pawn when you moved it there. To simplify, I'd suggest that any piece or pawn that is moved to the 8th rank will crossdress like usual, except that it can't become a pawn in this case.