In all my lurking and posting on WI forums and my communications with the experts, I've never heard of that happening, even spraying pre-rotor (Turbo'* can't spray pre-rotor, but we can).
Post-rotor is GENERALLY the preferred injection method, but as you can see, it can be quite difficult.
Keep in mind that water won't damage the epoxy coating on the rotors, and most, if not ALL the methanol will have evaporated by then. That'* the idea. As it evaporates, it cools the air/water mix. Evaporation removes heat.
Besides, you won't be running it that often.
Does this mean it won't hurt your rotors? Beats me. But I've never heard of it. I'll be doing it, because if it f'* something up, I'll get another used SC off eBay for $100 and start over.