Background: 2001 3.4l engine. Had a full overhaul on 2019 (5 years ago). Car has very light usage. Has run 20.000 km in those 4 years. The problem is, from day one motor was not ok. Had no power and blue smoke coming out. It has been progressing and this year did not pass inspection due to excessive smoke. A couple years ago a mechanic diagnosed it to be piston rings installed were incorrect. I want to takle the project myself as I have been doing most maintenance myself and have some mechanical experience.

The plan: Since the overhaul was done recently, I feel confident just replacing the piston rings may be enough. I dont think major damage may have been done for riding the car for 5 years like that specially it is barely used. So my plan is to just replace piston rings without pulling out the whole engine. This way I can avoid disconnecting the transmission. I can also have someone from the machine shop come inspect the engine once disassembled to verify previous overhaul still looks good and piston rings suffice. One of the concerns I have is if the machine shop guy says he needs to do something on the block, would I be able to pull it out without having to at least partially putting it back together?

How does that sound?

No way you can do that.

You would have to be able to remove the oil pan AND be able to remove all pistons.

It's doable on some motors but I'm not sure what the access is like on these

There's no way you could get a machinist to inspect the engine if you did it that way.

The amount of effort and headache that'd involve would be 10x that of disconnecting the trans and pulling the engine. If it's even possible, I'm not sure how you plan on getting them out without pulling the crank with an engine still in the vehicle. I've done that once before on a Cummins K50, which was a nightmare and involved sacrificing some rod bearings.
IF the problem lies within the rings its very possible you'll need the cylinders honed again too (which should really be done anyways along with new rings to ensure a proper seal), and the block would have to be out for that as well.
Compression and leak down tests would give you a better idea of where the problem lies.

Check compression on every cylinder and post up the results.

It's certainly possible, just not practical.

But you can take the heads off, and then take the oil pan off, and then undoing the rods and pushing the pistons up and out of the top (use a helper, lol).

At that point you'd have a pretty bare block with the crank in it. You're not really saving much effort in just pulling the motor out.

B4 doing anything I would do a compression test and a leak down test. If it is in the rings, Id pull the engine