I'm sorry, you did say you want to replace a small cabinet with a larger one (a duh on me.)
In any event, obviously, depending on how much bigger you want to make your cabinet, you may or may not be able to work with just 2 adjoining studs. I've got the feeling from (re-reading) your post that you'll need to go out one more stud. When you find this one-more-stud, you'll need to demolition all the way to it. Then, you'll need to 'cripple' the opening just as you would a standard, modern day opening. You should be able to find out how this is done on the WEB.
As I previously mentioned, once you find your left and right studs, and marked the opening. (The pros cut the opening with a reciprocating saw or the like). THey're careful in case there is piping or wiring behind the wall space they're opening up. (Good point: If there's plumbing or wiring behind there, you'll need to either re-do them around where you want to optimally install your cabinet or move the cabinet to a place in the opening that's not gonna with the plumbing or wiring. It's final location may NOT be to your desire. Plan well BEFORE you cut!)
Once you cut the opening, and cripple it, and find a spot for the cabinet, you rough-frame around the 'spot' and finish off the wall. Then, you put in your cabinet and (if necessary), finish off around it. I would suspect that if you're that interested in doing the wall's finish work, there should be books out there in libraries or book stores on restoring old homes. At worst, you can have a pro do just the wall and you can do the demolition, crippling, and rough-cabinet-finish work, and cabinet installation. Just my thoughts on this one. My best to ya and hope this helps.
PS: A site to visit (if you have the patience because it loads very slow right now) is The Ornamental Plaster. Brian Ewing has top-of-the-line advice and info at his site. It's a great one but again, it loads real slow.