Does clear silicone sealer damage stone?
The silicone will penetrate into the micro fissures on the surface of the stone. It will also be rather hard to get off once you attempt to remove the mats. You can get most of the silicon bead off with a sharp putty knife and/or a razor blade type window scraper. However the part that has penetrated down into the surface fissures will be nearly impossible to scrape off. You can try using a course steel wool pad that has been soaked in mineral spirits to attempt to scrub off the remaining silicon residue.

If you are ultimately concerned about the ability to cleanly remove all the silicon from the stone after the ice breaking pads have done their tour of duty then you should run some experiments before any mat installation is attempted. See if you can find any of the surplus stone material that was left over after building the steps or work on an out of view section of the actual step itself. Apply some of the candidate silicon and let it set up good for 4-5 days or so, Then attempt to remove the dried silicon and see if it is possible to remove it and all the residue.