If you want to try to follow the restrants of the jam you can uniformly edit a sprite as in any of the ways you can do it with pal statements or I think the 90˚ flipping or 180˚ mirroring is fine, normally in Pico-8 black by default is transparent so if you want to just use them the way they are you can set that to alpha if you want (though of course if you want to go nuts and not worry about it feel free.)