Repairing lath & plaster wall- structural elements
If the lath is rotted the supports are probably also damaged, I would add some temporary support inside by placing a board on the ceiling  close to the wall and one on the floor held in by studs wedged in place  (nothing nailed the top and bottom boards protect the ceiling and floor). It will take 2 people to do this and add enough supports to make sure if while removing the rotted material your wall will not sag, without support. I have repaired very old homes that the owner was trying to repair some dry rot and when he removed the external siding the roofline dropped almost 4 inches damaging the roof and the plaster inside. Once supports are in place the exterior can be safely removed and any rotten studs can be cut and replaced. When all the work is done the inside temporary studs can be knocked out and used on the next project.