Patching and Plastering - Lath and plaster

Hi,
I have a 1924 Craftsman with lath and plaster walls.
I'm thinking about insulating the exterior walls with either foam or blow in, but to do either I have to drill holes in the walls, a lot of them.
How hard is it to patch lath and plaster?
The holes will either be 1/2 inch with the foam, or 1 1/4 for the blow in.
Some rooms of the house are smooth plaster finish and other rooms someone has put on a skim coat of mud and some texture.
I would rally like to hide the many holes as good as possible.
Any ideas or can it be done?
Thanks!

I'm living in an old house like that too & I've given up on the idea of insulation. I haven't heard good things about foam or blow in.

I haven't heard good or bad, what have you heard?
I know foam can cost quite a bit and blow in settles but other than that I haven't heard much.

Smooth plaster over wood lath is easy to patch. When the holes are cut I think they will loosen a little of the plaster from the lath. Pull the loose plaster off and attach a piece of metal lath to the exposed wood lath. You can use screws or wire tie it. Paint the edges of the hole with a bonding agent like Plaster Weld by Larsens products or a similar product by quickcrete
For holes this small even though there are a lot of them I think I'd recommend for an amteur some Gypsolite or StructoLite and a little sand or raw gyp to get them to set. Screed them off flush and when the plaster is set finish them smooth with some joint compound, sand lightly, prime and paint.

Or here's an idea scrape a little recess around the hole to accommodate a paper flange and cut hot patches out of drywall and put those in.

I heard that it settles & doesn't provide much insulation & that the chemicals in it are very toxic. There was a segment on it on 60 Minutes many years ago.

OK, thanks for all the info.
Lots to think about, patching doesn't sound to hard to do but the texture might be.