Lath and Plaster

So if your working on an old house, and it has lath and plaster, that is wood slats with plaster on top, what should you do to mount a switch box in the ceiling. If you cut the board, the lath, you cause the whole plaster system to be unstable. In my case it was compounded by putting in a feed to provide the electrical wire to the box on the other end of the same piece of lath. Unwittingly I had cut both ends of the same piece of lath. After the fact I realized to put the hole for one end in one board and the hole for the other in another board. Granted you won't be able to get the two in line nice and symmetrical like an obsessive compulsive might want to see it. But given the choice between the plaster being sturdy with a board behind it holding it up or not and being in a nice neat line, I'd have preferred sturdy.
My very clever LW came up with the idea to put a piece of plywood over the affected plaster anchoring the loose plaster with liquid nails onto the plywood which was then holding up the liquid nails, paint, plaster to the beams the plywood was anchored to. The wiring boxes on each end were held in place onto the beams screwed in as a sturdy solution to replace the structural integrity which was lost by the lath behind the weakend plaster not being anchored to anything.
Still it would have been easier if someone had told me don't cut into the opposite end of the same piece of lath.