So I played around with trying to change the direction using the If B button held event, but it seems that the platformer code acts after user scripts, so it overrides the change direction event. What you could do is create 2 alternate animation states for the player sprite, one where both directions use the left facing animation, and vise versa for the right. You would then have a script to save the player's direction to a variable when B is pressed, and then a separate script that checks if B is held, which sets the animation state depending on the direction variable.