After you flip the order tokens and you get to resolving the March Orders and you have a march up against someone who has (as you can now see) properly defended the territory you wanted to march into and you can see that you may even lose the battle, can you just say never mind and do nothing?
In the directions it says: A player may move all, some, or none.. so it seems to me the answer is that yes you can change your mind but I wanted to make sure.
Thanks!