There are some that solder in choke tubes but to put in a threaded choke tube is not recommended
There are the soldered permanent tubes, and there are also permanent tubes installed with black LocTite. That LocTite has a specific designation, but I don't remember the details. Somewhere I have an article from years ago about that process, and I think the installation was in pattern welded barrels. I may be able to find it next week when I get back to that computer.
OP appears to be in the US, so British proof requirements are pretty much irrelevant, except from a cautionary perspective consistent with shooting all old guns.
As to why one would want to do this, my reason would be to put some usable choke in a Cyl/Cyl gun. Those chokes would make the gun useless to me.
