1. Shortening a rifle barrel is best done with power machines for a several reasons:
a lathe is quicker, more precise, and makes a perfect muzzle crown. downside: usually need to remove barrel. milling machine and drill press for dovetails and drilled holes. precise measuring and setup needed.
2. Hacksaw and file work can do a good job too, but is slower, requires more craftsmanship in measuring, and tedious muzzle crowning. Filing dovetails and drilling for reattached magazine tube also needs slow, careful work. Need special plug and bottoming taps in gunsmithing screw sizes, and drill press for barrel holes.
If you (or your gunsmith) are master class craftsmen, then an excellent job can be done using only hand tools.
For most everyone else, a trip to the gunsmith or skilled machinist is in order. I would guess that this work would cost close to $100 if professionally done.
HTH
John