Also, I don't know if it's the sort of thing that should be allowed to be undone, but I was playing recently and had placed my tile and meeple but had the option to remove a knight from a city because of the option of a Besiegers tile. I didn't want to remove any knights but it remained my turn while I thought about it, and I ended up changing my mind about where I'd deployed my meeple on the tile I'd just placed. However, from this point I couldn't undo and had to leave it where it was...