You should never attempt to cut or drill a magnet as most magnets (excluding flexible magnets) are very hard and brittle due to the manufacturing process. These magnets cannot be drilled with HSS drills or even carbide drills, they need to be drilled or cut with diamond tooling and plenty of coolant as the dust is flammable. The grindings are magnetic and within a few seconds of drilling the whole magnet will look like a hedgehog due to the grinding being attract to the magnet. It is much better to specify a hold which can be manufactured in and magnetised afterwards.