The bottom holes are offset on a lot of woodwind instruments of all kinds, coming from a lot of cultures/times. The reason is simple. It is the rest of the fingers that are used in a bent position. Point is, the "piper's grip" is not by any means "normal". In fact, it gets in the way of a lot of more sophisticated, fast techniques that are normal with, once again, a lot of woodwinds. Fingertips are simply more flexible. That's why, in a word.
Now, as to the point. The way to do what you asked ( taking an existing chanter, and making the bottom hole revolve) is not impossible, but is rather a pain. What it involves is taking the chanter, putting it on the lathe between two centres, praying that it has not gone out of true shape too much (a rather futile prayer, to tall the truth); then cutting the bottom part off half-way between the two last holes (still on the lathe, that is.). Now, next step is putting the two parts back on the lathe between the two centres, and turning a tenon on each, just a fraction thinner than a (yet to be explained) socket's inside diameter. The socket in this case should be a brass (silver, gold, whatever) tube, about 15-20 mm long, the outside diameter of which is more-or-less equal to the outside diameter of the chanter at that point. The tenons on both sides should be turned with a small recess to take cotton (waxed cotton, that is) binding. These both fit tightly into the brass socket. The length of the tenons put together should equal the length of the socket.In theory any competent turner should be able to do it, but in reality I'd prefer to trust someone who has experience with woodwind instruments.
Where are you located?