Re: Turn/rotate pickup? I'm curious..
When two humbuckers are on together, they are in parallel WITH EACH OTHER. But each humbucker is still both coils in series.
But you CANNOT reverse the phasing by just turning the pickup 180 degrees. Phasing is electrical, it's not about physical positioning.
The one exception to this is if you had one pickup ABOVE the strings and the other below. In that case they are reading the string vibrations opposite each other -- on the same vibration, the string is always moving simultaneously toward one pickup and away from the other -- so they are then once again electrically out of phase, one pickup generating a positive current, the other negative.
(I know this from hard experience because I drove myself crazy one night trying to test a pickup without installing it by holding it above the strings with the other pickup in the guitar. I know I wired this @#$% pickup right and have the magnets facing the right way (checked with polarity tester), so why are they out of phase??? So I put the same pickup IN the guitar with the other pickup without reversing the leads or flipping the magnets, and whaddaya know, in phase again. Try this sometime if you're bored. Or not.)
But since no-one ever installs pickups above the strings because it's obviously extremely impractical and pointless, this exception is purely academic. On the same side of the string, the physical positioning of the pickups have ZERO effect on phasing and polarity.
As for whether there will be a tone difference when turning the pu 180 degrees, there will. How much depends on a bunch of things, like whether the coils have more or less the same number of turns, or are wound deliberately with one coil significantly hotter than the other. Or if the slugs and screws are the same alloy or different alloys, etc.
Obviously how high the screws are adjusted will make a difference too. But assuming the screws and slugs are set equal in height and the coils with the same number of turns, the slug coil would be just a bit louder in the same position than the screw coil. (Not a radical difference but some, though likely unnoticeable with anything beyond light gain.) This is because the screws drag some of the magnetic field below the baseplate and thus further away from the strings than the slugs do. The slugs also are thicker top to bottom than the screws, so they'll see more midrange and bass.
Finally, there's no reason to yell at anyone or try to chase them out of a thread for being wrong. Just gently correct them and move on.