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Sorry for my ignorance, but does this become less risky when moving the root file system from flash to the sd card as in http://forum.arduino.cc/index.php?topic=236696.msg1701441#msg1701441
The link you provide will give you "pivot overlay" and not complete root file to the sd card.
for complete root file - "pivot root"
http://forum.arduino.cc/index.php?topic=228204.msg1651254#msg1651254
http://forum.arduino.cc/index.php?topic=228204.msg1653830#msg1653830