"Break in" implies there is change, as in a perceived improvement. To effect that change it follows there must be a physical change to a passive component operating well below it's design limitations... in this case the wire. DON'T BE RIDICULOUS! If your premise were true, we would be awash in "improvements" to Ohm's law.
Yes, I am an engineer. No, I'm not closed minded. Im' just not inclined to re-prove established facts whenever a doctor, lawyer or an executive banker takes notice of what I do, day in and day out.