For breach- seat throats a separate throating reamer is almost always used. 

40 Rod

Throating is never a good idea if it is a 100 year old rifle. You can get the same effect by getting a custom bullet mold that is either 2 diameter or tapered. If it's a new barrel-who cares. Go for it.

I think that it'd depend a whole lot on the way the original is set up and how you are going to shoot it.  start with a good chamber cast and see what you actually have before doing anything.
As I understand it.  The point to "throating" is to break the angle of transition very slightly ease the effort to seat a bullet into the rifling if it is loaded long or breech-seated.
With mechanical seaters, soft alloys, tapered cast bullets I have a hard time imagining a need.
However if you are shooting jacketed or real hard cast bullets for higher velocity and shooting fixed ammo I can see where you might want to consider it.  (Even with hard alloys a change in mould configuration and/or a longer lever on a breech-seater might solve the problem)
As Ken says, you do NOT want to mess up a quality antique gun when an alloy change or a better fitting mold will do the trick