If you planned it out right, it might be possible to get the info back to the batter in time. Back in the day, teams stealing signs would send them back to the batter via things like a light on the scoreboard. Once the spy has the signal, the batter could step out of the box or adjust his batting gloves until the signs get back to him. Sure, the catcher could change the sign after that, but the hitter will have a bit more of an insight into the situation.