I've worked with plaster a little before and not been entirely pleased with the results. This job is very high profile, and I don't want to make our dining room look worse than before. The hardest problem I have always had with plaster repairs is cutting a straight, square hole in it with a keyhole saw. No matter how hard I try, I can't cut a clean hole through the stuff. The wood laths always vibrate with my saw strokes and crack the plaster further out. Not to mention the number of keyhole saws you go through doing that.
I'm considering using a sawzall, but I'm not certain that even that will work. If I saw through all the layers of plaster and the lathing in a square outside the damaged area, would it help to deeply score a line or lay down masking tape, or is there another way to help improve my chances on making a nice, square patch? If it is a good idea, any particular type of blade the best?