I would think that you would have to find someone in the area that the cemetery is located, have a photo taken again to double check that there isn't a Q. Then get in touch with the person who put the tombstone up in question and explain what happen. Then offer to pay for the correction to the tombstone. I would think that whoever bought the tombstone owns the tombstone. I know that I would be upset if I visit a family grave and found changes to the tombstone I bought. Just a thought.