They only have one magnet. The poles from one coil touch the North end and the poles from the other coil touch the South end. It can be rewired to operate as a single coil if the pickup has four conductors. If it is a two conductor pickup there are people that offer service to rewire to four.
Hmm... The only "outlandish" way I see to turn a humbucker into a single coil pickup is connecting its coils in series/in phase and using same polarity bar magnets for gaussing them