I’m sure it’s possible that the bearings in the motor can do some form of “break in” as well as the suspension ( if it has some). Certainly, the cartridge, just like a speaker but in reverse, which converts mechanical energy into electrical may need some break in.
There are those who think wires & cables break in too & although probably not measurable, might be true. I think this also be a matter of our own internal “wiring” meaning our brain & nervous system getting used to new & different sound.