Re: "Pickup Break-in" Any truth here??
If you consider that a pickup would not function without a magnet, to me it's tantamount.
Right, but what I'm saying is that it's not the entire pickup "breaking in" but a newly changed magnet settling into its new environment.
Maybe it's because I think of "breaking in" from an automotive standpoint. Every time I've built an engine (which sadly, hasn't been for several years) there was a break in period. Quite literally you're putting some wear and tear on certain parts of the motor to cause them to work well together. Cylinder walls smooth out, piston rings form to any irregularities in the cylinder walls, bearings form themselves to the surfaces to which they're mated, etc. You have to go easy on an engine for a little while so you don't throw a bearing or cause some blowby with a piston ring. However, you can't just let an engine sit there and it'll break in by itself.
Or, maybe, thinking of breaking in like a nice leather jacket. When you buy a brand new leather jacket it's fairly stiff. That leather needs to be worked a bit. Worn. It'll take the shape of its wearer to a degree (in my case, potato shaped). It'll soften up, become more flexible. The color will change slightly. Again, not something that'll happen if you leave it on a rack.
Changing a magnet... You swap the magnet, you let it sit there. It goes "Oh, hey, pole pieces, baseplate, keeper, and the rest of you ferrous parts. What's up? Mind if I join the team? Let's integrate!" Things shift a bit magnetically. However, this requires no intervention from you.
As far as a pickup breaking in, under normal operating conditions the magnet may degauss SLIGHTLY, but nothing really noticeable. Those trying to relate sticking a pickup by a large speaker and having it degauss and calling that breaking in wouldn't call falling off your motorcycle and causing tears in your leather jacket breaking in, nor would they cause revving the snot out of an engine during the break in period and causing rod knock to be breaking in. I consider that to be incidental abuse, not breaking in or normal wear and tear.