I wish GFS were a bit more explicit with how their bass pickups are configured and can be wired etc., it would save a lot of hassle.

MM pickups are traditionally wired with their coils in parallel, which makes it easy to connect them to blend pots etc. However, the GFS MM Pro actually has its coils wired in series, like a standard humbucker, which makes using a blend pot trickier... but not impossible.

With parallel coils, or two pickups in parallel, a blend pot controls how much signal from each goes to ground and how much goes to output. With coils in series, like the GFS MM pup, the blend needs to work more as a fade/bypass and control how much signal goes through a coil and how much bypasses it. This changes the way things work a bit and how you need to wire the blend pot, but it’s doable. If you want I can sketch up how you’ll need to configure it (which should work) but it may take me a day or two to get time.

If you just want to cut one coil then that’s easier, it just means you’ll only use half the blend pot.