So I have a building from 1910 that needs a lot of work. My intent is to update the plumbing to copper and to completely replace the electric. The plumbing isn't much of an issue as I will likely bring the bathrooms and the kitchens down to the studs and start over, this makes my plumber & electrician very happy. However in all the other rooms I will likely cut chases in the walls for outlets and switches.

The city of Chicago wants all electric run in conduit so I can't just pull romex I have to pipe the whole place, this is not a big issue. The question I have is how to repair the chases I'll have to cut into the plaster walls. From what I call tell they are horse hair plaster (1/2") on wood lath (1/4"). I don't want to cover everything with 1/4' drywall as it affects the look of the trim. I'm going to hire a skim coater but I want to know the process. Will they just cut strips of plaster board, fill in the chases and the skim coat the whole wall or is their another method?