"Burning in" your cans absolutely changes the way the driver physically reacts to signal.
The edge of the surround of the driver becomes a bit more pliable along the glue line.
Also, any driver with a treated paper or rubber (goop) impregnated cloth surround becomes more pliable as the compounds mollecular structure becomes more pliable and evenly deflected.
Bought a pair of AKG 271 and thought the things were a bit slight on the bottom end, like quite a bit.
Made a tone sweep file with my tone generator with slow sweeps from 15Hz-10KHz.
Let that run through them at a moderate level for a few days and it really improved the low end response...
This is sort of like running a stiff new shirt through the dryer for a while, although I would refrain from tossing your cans in there with your shirt.