I did a house a few years ago that I replace 24 doors total (including sliding doubles for closets in 5 bedrooms). So 14 doors that I had to chisel out hinge sets.
So here is what you need to think about:
Can I get doors in the correct width? Cutting a half inch out on the hinge side will be fine. Once you get more than that there are issues (tell you later).
Can I get doors the correct height? Unless you are getting completely solid doors You will have about an inch at the top and bottom. So about two inches to play with.
Is it feasible to make the lockset fit in the same opening? Are you getting doors predrilled? Does the predrilled holes match where your current lockset is?
How level is your house? How square are your current doors?
How good of shape are your current jambs?
I can tell you in detail what you need to do for each door but the gist is, you measure old door, cut new door. Visually everything starts from the floor so you want to be either cutting the top or bottom consistently.
Then you have to take a hinge that you will be using and draw your aligning hinge sets. I also use measurements for old door - this is way way faster.
Score, chisel hinges. Once you understand how to do this you can do each hinge in about 5 mins - there is a specific technique (not in video above) that ensures a better fit.
Probably drilling holes for new lockset, installing door, and installing lockset.
Then you have to go back over jamb to fill the other hole... And done.
Here is the big big problem. Unless you are paying over $200 per door your casings will suck. All the big box casings are builders grade or less unless you get a premium door.
Pros for swap everything...
- Door should fit right on first try or should be quickly realigned.
- Will not have to fill the lockset holes.
- Will not have to buy an electric planer. Doing your own doors your cuts are so exact. Too much and you can see the other room, not enough and the door sticks. And maybe you don't know if door sticks until season change or coat of paint. You will be planing parts of the door for sure just doing the doors.
Cons for swap everything...
- Costs more - a lot more.
- Your jambs may not be as good of quality.
- It takes more time for sure. Let's say 2-3 times more. You have to demo too. And if you are slow just installing the door, installing the whole thing isn't going to make you an expert. Your last doors will be done in half the time as the first few.
- I wouldn't cut new door sets except height so if you have weird widths you might need to reframe (or should).
- It holds up everything else. If you are replacing trim everywhere, you must wait for that section until door is swapped. If you just replace the door itself, it doesn't matter.
So on the 14 swinging doors I replaced I would say that 10 were installed really well and look original. 2 were not squared and took me FOREVER to get right. Like 2-3 hours per door. 2 I was a tiny bit off and they ran a little small. I might be the only one that noticed but I noticed and I wasn't redoing them.