i don't know anything about gunsmithing and headspacing threaded barrels.
changing barrels on encore's and contender's is simple and anyone can do it in just a couple minutes. all you do is remove the forearms two screws, break down the action(like you were going to load or unload) and gently tap out a round hingepin. the barrel comes of and goes back on the same way. very simple.
now if you are wanting to make barrels for the encore, it is very complicated and would require welding a lug on the bottom of a blank. which would be a higly specialized task, and require a custom shop that does that sort of thing. two that come to mind are virgin valley custom guns(
www.virginvalleyguns.com) and bullberry barrel works(
www.bullberry.com)
hope this helps and answers your question.