Actually, as OA points out, freezing them - especially quickly and at extreme temperatures - could harm them.
My initial take is that this is hype. But there maybe some effect if the enamal wire coating did crack all through the windings and there are now random shorted coils throughout the pickup. Would it sound "better"? Or just different?
I am a bit incredulous at his claim of seeing an 18% increase in output though...
I still love the Callaham steel tremolo blocks though.