Thank you all for this information. I will pass it along to my friend. It is her ggg grandparents grave, so I don't think ownership is an issue (but not sure, so I wouldn't even assume that), but I know she absolutely doesn't want to damage the stones. I am in the US and don't know anything about lichen being protected, so there is another thing to look into. I knew I was posting in the right place.

I will let her know.
On a side note, I am going with her to visit an old family plot, which will entail a hike to get to, and I am so excited. Her family has been in this area for generations and the original family member who settled here is buried there. Not my family, but exciting to make the excursion with her.
Thanks for all the info and especially the cautions.
Kath