Changing the subject slightly, http://en.wikipedia.org/wiki/Runway says
"Runway designations change over time because the magnetic poles slowly
drift on the Earth's surface and the magnetic bearing will change. When
runway designations do change, especially at major airports, it is often
changed overnight as taxiway signs need to be changed and the huge
numbers at each end of the runway need to be repainted to the new runway
designators. In July 2009 for example, London Stansted Airport in the
United Kingdom changed its runway designations from 05/23 to 04/22
overnight."