Unless the paint on the siding is flaking off or chipping I would not worry to much. The asbestos in the siding and roof shingles is in the insulation barrier (the middle) of them so unless they have severe degradation I would say you'll be fine. JUst try to stay off the roof as much as possible. They stopped using asbestos in shingles in the early 80's so keep that in mind. Just remember it's easier to increase your solution % than decrease it so start off light on your mix , hope this helps.

Almost forgot to say if the paint is peeling on the siding and you know that the siding is asbestos then theres about a 100% chance that the paint is lead. If it is then you'll need to get the permits and proper paperwork done for the lead paint removal. Even if you are just cleaning the siding and the paint starts chipping off you'll be held liable for it hitting the ground which falls into the category of lead abatement and you need to be licensed to do that in most places.

I would pass, too many dirty roofs with far less liability.
Although I understand its for a friend so just don't agitate it at all.

Thanks guys...I tried a little test spot and all it did was turn the mold orange. I am really curious if I increase the SH% if it will ever come clean to the point that moss will be gone.

It should come clean. You might try another application in the same spot andsee if that helps.