This is where the roto zip is your friend. I use a tile bit to cut out the plaster then a wood bit to cut the lathe. It is the least damaging way to do it as the cut comes out perfect. Then I follow up with some #4 wood screws.
I also always tell the customer old plaster is just that, old and damage may happen but i do my best to minimize it and would patch it if I did damage. It's part of the job
