I've wondered about that, if taking a gun apart might change the POA-POI. Can you do a full nickel or full blue finish without removing the barrel?
Sorry, late to the party.
Yes taking the barrel off will change the POI/POA unless the smith is extremely diligent about marking the frame and barrel and then very carefully putting the SAA guns back together exactly as it came apart. Having seen dozens of SAAs taken apart for engraving and-or refinish work my experience is few can be bothered or care about guns ..."most don't actually shoot anyway." That simple lack of detailing is the end result I have seen no matter who is involved or the price tag of the finished product.
You can full blue or nickel (antique or electroless nickel are better answers here but still not the best way to do a refinish) with out removing the barrels but it is a half assed job that a really good refinisher wouldn't generally offer or accept.
Here I a classic example of " the best" workmanship when it comes to putting a Colt back together and what it takes to get right again.
To get it right you'll need ammo, patience and a good barrel vise. Easier than it sounds for sure. It's not pretty and
really disappointing on what should be an heirloom gun out of the box for the price. How the gun shot as delivered from the engraver/refinish on the left. On the right is after turning the barrel back to vertical where it started out from Colt. How the gun was delivered is nothing more than basic pistol smithing work done at a
rank beginner's level. But the targets should give you an idea of what refinishing a good gun puts at risk.
This is a 25 yard target I shot, sitting, over the top of my range bag from our China Camp in 32-20. I don't know of anyone including myself that I would trust to pull this barrel and screw it back on for this kind of POA/POI accuracy. So I just take the time to rub the bare metal down with some oil to keep rust at bay. That plan has been working for over a decade now, so good enough I guess.