I have successfully hacked my Paperwhite 3 to have a black power button. I don't think has ever been done successfully. Yes the power button still works 100% and no it wasn't painted. It makes the bottom of the device look MUCH more symmetrical.
Also Amazon GIVE US 5.12.5 for the pw3
I would be happy to write a guide if anybody is interested. This hack doesn't take more than 1-2 hours.