The very, very thin threaded area at the yoke cutout makes changing J frame barrels very chancy. The area doesn't support much torque on the barrel and it's extremely easy to crack the frame while installing a new barrel and/or removing one. You may not crack it right away, but the crack will appear in a box or two of ammo.
If by some chance your J frame has an aluminum frame, I've been told the factory won't try to change those.
If you decide to try it anyway, take pictures, make sketches, mark the frame or whatever to record the position of the original barrel when it's hand tight on the frame. If the new barrel doesn't come up to the exact same point at the same pressure, take your project to a revolver smith or send it back to the factory. There isn't a heck of a lot of rotation between hand tight and lined up. There also isn't a heck of a lot of difference between just right and buying a new frame.