So I tried this and I'm no longer intrigued
I took all the screws from the coil and then played the guitar and switched between split and full modes. I use DigiTech Genesis 1 on the Brit Stack (crunch) and Black Face (clean) settings, with a British 4x12 cab model to evaluate tones of my guitars.
Well, with the screws out, the difference between full HB and split modes was barely perceptible, I'd say the split mode sounded like 10% more trebly and wire-y. But I wouldn't take this to the bank.
So the poles went back in and this time I screwed them all the way down into the bobbin (I had to gouge out some wax first). I played the guitar through the Genesis again, and to be honest, I wasn't sure anymore what I was hearing and how it compared to the other settings that I had tried.
So I just adjusted the pup and polepieces as high as I could to get as much juice as possible without the magnetic pull getting too annoying, and left it at that.
No disrespect to exercises like this - if you have good ears this can make difference. But for my part, I guess I just have listened to too many heavy metal records through my headphones to tell the difference anymore.
OK, back to work now.
Later
Tony