Arduino Micro: how to switch off its blue power LED?
Unfortunately the blue LED is a direct connection between 5V and GND. You can see below in the schematic exactly how it is connected



The only way to 'turn off' the LED would be to remove either the 1K resistor or LED with a soldering iron.

Another possibility is to take a sharp knife and make a cut in the track directly before or after the LED. I've marked the locations where to cut on the eagle screenshot.