For the first part of a move, use usual algebraic notation. The context will make clear what is going on. For removing a Pawn, use x location. For example, x a1 means a Pawn at a1 has been removed. This game will last no more than 32 turns.
Pawns demote only once, disappearing upon demotion.
As pieces change sides in orthodox chessgi fashion, the number of turns available to one player will increase. But this won't cause the game to last any longer than 32 turns, because it comes at the expense of the other player's turns. When the player with fewer turns left is reduced to a bare King, the game ends with that player losing, and this will always come before 32 turns are up. So that Pawn promotions will not increase the duration of the game, Pawn promotions are drawn from pieces held in hand by one's opponent. Without the extra Pawn held in hand at the beginning of the game, this game would last no more than 31 moves.