At this stage, changing the superficial elements is relatively easy. Relatively. Also, it just pushes me to accept what I already knew: a certain aspect of my book was not quite fresh enough.
I still believe that the key concept and the (hopefully) frankness with which I hope to approach it is fresh enough in a fantasy setting. I have to plumb that concept to find a MacGuffin that will lend resonance to the story as a whole.