I'm currently making some hybrid humbuckers. For years I had thought that it was hard to do, but actually it's pretty simple.
The wiring color codes go like this on Duncan HB's:
- Screw coil - top coil wire goes to red, bottom wire to green.
- Slug coil - top coil wire goes to white, bottom to black.
You can easily swap slug coils between Duncan HB's and reconnect them following the wires codes above. With 4-lead HB's, it's quick to do. If one or both are single lead, you'll need 10-14" of 4-lead wire. The color code connections are the same to the coils, so it's not confusing. Screw coil: top wire red, bottom green. Slug coil: Top white, bottom black.