Replacing the barrel requires a special tool to unscrew the muzzle nut, slide off the shroud and unscrew the barrel. Replacing is the opposite and requires a leaf-type feeler gauge to set the gap. If it is truly "new in the box" the tool and gauge will be included. CZ Arms still has a few parts for these revolvers.
On a personal note; given the amount of time these revolvers have been out of production and the fact that, until recently, they didn't command the highest resale value, except for the specially engraved collector models, I seriously doubt there is an actual "never been fired" Dan Wesson on the planet.