When the Front Yard Retaining Wall was built, I first put all the stones in place, to make sure that I had enough stone, and that my levels were right -- to be able to see what it would like, roughly, before it was fixed in place. It was just meant as a proof of concept, but the masons took it as literal and tried to use the same stones in the same place, taking it apart and putting everything back where it had been.
Unfortunately, I didn't pay that much attention (well, no attention) to exactly how it looked. And the result, after it was all in place, was that three of the stones on the top had a backside which was less than perfect.
This would not be a problem except on the top course of stone, where the top edge of the back side of the rocks shows.
It seemed to me that the easiest way to fix that would be to replace these stones. So I measured them, and went to Whittlesey Landscape Supplies, where I had bought the original stones, and got stones that were just the right size for these 3 stones, and placed them on the wall above the stones they were to replace.
Months later, when there was basically nothing else that needed to be done, on a dreary day, I had the guys come back and replace the stones. $350.
They started with the new stones.
and broke apart the old stones to get them out of the way, chiseling the mortar out to get a smooth place for the new stones. Then they spread the mortar and put in the new stones.
This gives a much smoother inside line.