I live in a 1926 bungalow where the insulation has settled over the years and need to insulate badly.

My interior walls have this beautiful "scumbled" plaster finish [not smooth] so drilling holes in between the studs will leave nast unrepairable scars. The men who finished the walls are most likely in the grave 20 years and I'm confident there's not a person alive who will be able to cover the scars left behind. After much research I've decided I've settled on the possible solution.

Can I remove the soffits, drill down through the top plate on the wall and spray foam insulation in the cavity. If so, how do I gauge the expansion rate for the wall? Is this a bad idea?

Thanks