curious about something. First, how far back does the additions go.I would jack up the corner but that is all I would.as far as jacking goes. If it was me, I would go about this by taking the floor out. Then I would put plastic down,run new wire and plumbing. While you are there, check all joist and repair if needed. I really think this would be easier in the long run. Consider this, the house has been there for 130 years and your only real concern is one corner is sagging. Also,your right,do not let the contractor bring dirt closer to the frame of the house. I hope someone will cut in here and correct any thing that I said if I'm wrong. Post back and tell me your opinion of this route. Ron J.