I've done that with many C1's and C2's. Its mildly beneficial. The tone is a bit stronger. But the design of those stacks is such that the magnets do not go through the second coil, so eliminating the second coil has less of an effect on the tone than, say splitting a "rails" or a traditional humbucker. I know, you mostly want the hum-cancelling effect
That is a multi-part endeavor. I'm going to give another long winded answer. The Cx pickups are wound to work only one way. You can't reverse the phase on them as a whole. (you can, but it's not designed that way) See, there's a metal shield/magnet "focusing" wall on either side of (and between) the coils. It's wired to the red wire and is grounded. If you reverse phase and make red hot you just activated that shield to increase noise and reduce its effect.
That being said, the pickup is also wired so that if you short one coil by jumping that black junction to ground, you get the bottom coil.
With no magnet in it and at 5/8" from the strings, it's almost dead. To obtain the top coil, you either have to jump the black wire bridge to hot, or a double switch where you take the appropriate black wire to hot while disconnecting the green hot. (don't waste the time, the first is fine)
If you are automatically switching your hums to single mode with your 5-way, you'll have no switching options left to perform this task. You'll need a 4-pole switch, like the Yamaha or Ibanez one. Wire the hums as usual, then use one of the other "switches" to jump the coil junction back to the middle pickup's own hot, not the switch hot. This could produce an out of phase/non-hum-cancelling sound with the humbuckers (as singles). I can't remember if this surgery is in phase or out of phase with other Dimarzio humbuckers. If you want to cancel hum, just switch the ground wire that splits the humbuckers with a hot wire. That will give you the other coil, and cancel hum. Or reverse phase of the hums. You'll still get the other coil. If you want the same location coil still, you'd have to spin the hums and the logos would be backwards.
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