I have no issue with completely disassembling and reassembling S&W J, K, L, N frames. It does take at best a good screw-driver and skills to use it -- which many people overestimate themselves for.
Now replacing parts or fixing issues with them "depends." Doing simple replacements like springs are a "drop-in" job. Replacing a part that doesn't include a sear surface or involve timing is also probably just a drop-in. Sear surfaces like those on the hammer and trigger could be drop-in, especially with MIM parts, but not necessarily, not even with MIM. Timing parts like the ratchet and hand also have to be carefully fit. It's possible to get lucky with a drop-in replacement, but it would only be fitting by accident.
The real problem with revolver service is that often times it involves more than just parts replacement, even if the parts are fit. Revolvers have a lot of parts that work together. So if a part has gone bad and needs replacement, a new one often cannot be dropped in without adjusting everything that interacts with it. While these adjustments are not beyond the home gunsmith, they often take special tools and fixtures to do them best. Some examples: you could swap out a bent ratchet and ejector rod, but you'd have to adjust the timing by fitting the hand to the new ratchet. Alternatively, you could just straighten the existing parts, but you might want to use a Power Custom Extractor Rod & Yoke Alignment Tool. Then you might realize the rod is stuck. Bubba's gonna just bite down on it with his Vise-Grips, but it's better to have an Extractor Rod Wrench Remover. Now maybe the extractor rod is straight, but end-shake is excessive. You'll need shims and probably also a hammer boss cutter/yoke cutter. Working on the hammer or trigger? You'll want a Stoning Fixture with the correct adapter plate for the parts you're working on.
Then there are jobs like barrel replacement. On an automatic, that's just a drop-in job, as easy as a field-strip. With a revolver, it's going to take a barrel wrench and a fixture to hold the frame properly. The barrel has to be threaded and clocked just right. Then the barrel face has to be machined-off to the correct barrel/cylinder gap and the forcing cone recut. Again, this takes skills and tools. Imagine if there was an automatic that didn't have the chamber machined as part of the barrel but the end-user had to do that or get two separate parts to fit together. It can be done, but not without a substantial investment in specialty tools and some skills.
One of the common jobs I've farmed out to gunsmiths on my revolvers is cutting the cylinders for moon-clips and having the chamber mouths chamfered. There is a chamfering hand-tool available, but cutting for clips takes a mill. Together, it's really best done by someone with a CNC setup configured and programmed. Then it's a push-button job, but that's not a setup a typical end user is going to possess.
