Yup! I took one apart when I realized that I forgot the sashing. I had about 1/2 of it together at that point! But it looked so much better with sashing! I was happy to finish it appropriately and send it on it's way to it's forever home!
If I ever were to donate a UFO, I'd feel compelled to donate the rest of the material that I was using to finish it too. That way if the future owner of it wants to finish it, they don't have to try to match fabric.
I'd like to see what your finished pinwheel looks like now that you've finished it!