If the barrel is offset you would have to remove and replace the lug.
the lug could be ground and rewelded to put the firing pin in the center of chamber.
Im not making myself clear i guess... if 17hm2 was centerfire, the firing pin would strike the primer as it is. but since 17hm2 is a rimfire, the firing pin strikes the center of the casing.
No, you didn't state what gun you are fooling with. Visit www.go2gbo.com and visit the forum for NEF guns. There is far more info there than we could ever discuss in this thread. I will say that you don't just arbitrarily change barrels and frames on those guns, there is a fitting procedure that must be followed for safety and function. Good luck. Goatwhiskers the Elder