I have had very good luck in swapping S&W parts between guns (forget doing it with Colts). I once replaced a bulged M&P barrel with one I got for $5 off ebay (this is where people start howling about how you can't replace a barrel at home without ruining the frame but somehow I managed to do it and frankly it wasn't that big a deal at all). I soaked the disassembled frame overnight in penetrating oil and after driving the barrel pin out with a punch I clamped the barrel between two pieces of wood in the jaws of a large vise (remember, people will say to not do this) and inserted a large wooden handle through the cylinder window. I pushed the handle up close to the forcing cone so that the pressure would be exerted near the front of the frame to lessen the risk of twisting it. It unscrewed slick as a whistle. I really don't think I put more than 5 pounds of pressure on it.
People are right when they say you can damage the frame doing this but I worked carefully and had no problem. It was an $80 gun and the smith wanted $100 to do the swap. That made no sense to me so I figured I had nothing to lose by trying it myself. On a nice gun I would reconsider.
The replacement barrel screwed right in and I snugged it in the vise. Total time for the swap was about 3 minutes. I then spent 45 minutes trying to tweak the barrel into just the right spot to reinsert the barrel pin. Definitely the most trying part of the whole exercise but I did finally get it in. It was frustrating, though.
With the barrle pinned and the front sight blade straight up the barrel/cylinder gap measured .004" and I was good to go. You can't count on always being this fortunate but it worked for me. Gun shoots great.
I like the wide, smooth trigger and have swapped many of them onto my N frames with no professional smithing required. I have installed maybe 12 such triggers and only once did it not function fine as a drop-in replacement.
One of my 27s developed an awful rust spot on the cylinder. I bought a replacement in perfect condition from a used parts seller and it dropped right in and worked fine. You'd never know it wasn't the original.
Last year on one of these forums someone asked the very same question you have about creating pintos by swapping parts between blued and nickeled guns so I tried it. I took 2 of my 27s (one blue one nickel) and swapped the cylinders. They fit and worked just fine.
Used replacement parts don't always work on S&Ws but in my experience they mostly do. Get a blued M10 and a nickel one and I bet a smith could easily swap the barrels and cylinders to create a pair of pintos.