Disclaimer- I am NOT a gunsmith (God knows!) I would hire a competent smith who has a good shop and can use a lathe. Issue is not just threading the exterior, but threading it so that it is exactly in line with the bore, and not canted in any way.
Unless you are a tool and die maker, I would not. At best, you will save yourself a few $$. At worst, you have an unsafe firearm. In the middle, only a messed up barrel that would need replacing.
What we have heah is.... failure to communicate.