I think this is against leather care guidelines -- water and heat will dry out and mess up boots! Do you have any conditioner - Leather Honey, mink oil, etc? If so that would help a lot to fix up the leather and then prevent future stains (as it waterproofs the boots).
Yes, I'm sure it is. They were going into the trash otherwise. Water spot was big and very ugly.
I have many conditioners and oils and use them generously on my dark ones. However I spot tested it on those and it grossly discolors the light boots. I'll never buy boots this color again.