What do you think permanently changes electro-mechanically during this mythical "break in"?
The mass of coil and diaphragm? Can't.
The compliance of the surround? Won't.
The resistance, inductance or capacitance of the coil? Can't.
The shape or size of the chamber? Can't.
The magnet strength? Won't.
The coil/magnet coupling? Can't.
The relative placement of interacting parts? Won't.
The stiffness of the diaphragm? Won't.
I think that about covers all the possibilities. It is far more likely that the listener's perception changes due to expectation. Far, far more likely.
The mass of coil and diaphragm? Can't.
The compliance of the surround? Won't.
The resistance, inductance or capacitance of the coil? Can't.
The shape or size of the chamber? Can't.
The magnet strength? Won't.
The coil/magnet coupling? Can't.
The relative placement of interacting parts? Won't.
The stiffness of the diaphragm? Won't.
I think that about covers all the possibilities. It is far more likely that the listener's perception changes due to expectation. Far, far more likely.