1.) You'll never see it. And be glad it's new. Old stuff can be a b!tch....
2.) If you sureform this thing, you'll be at it forever and making a huge mess!!!!
3.) Try my idea of cutting back the rock. If it doesn't work, then go with the extension jambs. The problem with an 1/8" extenstion jamb, is that it's a little sliver of wood and it can be a PITA to work with. You have to offset it. Don't run it flush as suggested. You'll always have a seam.....
4.) Trust me.....I've been a remodeling trim carpenter for a lot of years.
BTW .....you keep referring to an Exacto knife. Not to be critical but I think you're referring to a Utilty knife
One's for model making and crafts the other is for cutting back sheetrock to make your trim fit perfect.
In my case, I don't understand why I never noticed it before. I think whoever built the house way back when used spacers and they fell out or were torn out when I removed the old paneling and rock in the bdrm. I am pretty sure the bow in the wall near the door was not there. Its like when the framed the rough opening for the door, they offset it just a little or used bad lumber.
Anyway, I have the new jam out and trimmed down. I will figure what to do with it in a day or two. If I didn't feel like the header would cause problems, I might would use my multi tool and do some back cutting on the rock...naw, that would just make the 16" or so bow show more.
While I am at it, I may very well do some more removing of rock, the new and the newly skimmed in the foyer, and rebuild that side of the door opening.
My wife says I expect too much, maybe I do. Since this mine, I may not go to so much trouble.
Heheh, just according to the mood I am in when I get back on it. Can't be long, I have the jam standing in the opening with cross pieces tacked to it to help keep it square a nd flush with the wall on one side.