Modify Bluetooth plist DeviceCache and retain changes?
I found the answer!

Mavericks caches preferences so you need to load your changes into Mavericks' cache.

The key is to do: defaults read /Library/Preferences/com.apple.Bluetooth.plist in terminal after making your changes to the bluetooth.plist and before turning bluetooth back on.

See here: https://github.com/OpenEmu/OpenEmu/issues/1041#issuecomment-39808894 for a full writeup.