Has it be done before?

[Metallover]

The magnets don't like being machined either. It would really be risking it if you tried to hammer it off or something.

Heres some info from kjmagnetics.com. The sell the same type of magnet used in brushless motors. You won't be able to buy anything for your motor, but they have some fun magnets and good info.

-17. Can I cut, drill, or machine neodymium magnets?
The Neodymium Iron Boron material is very hard and brittle, so machining is difficult at best. The hardness of the material is RC46 on the Rockwell "C" scale, which is harder than commercially available drills and tooling, so these tools will heat up and become damaged if used on NdFeB material. Diamond tooling, EDM (Electrostatic Discharge Machines), and abrasives are the preferred methods for shaping neodymium magnet material. Machining of neodymium magnets should only be done by experienced machinists familiar with the risk and safety issues involved. The heat generated during machining can demagnetize the magnet and could cause it to catch fire posing a safety risk. The dry powder produced while machining is also very flammable and great care must be taken to avoid combustion of this material.