iOS (Jailbroken): When selecting a Bluetooth device in iOS, a pre-defined named is saved on your phone and there's no way to change it directly from your device. This is annoying if you have a few wireless speakers, for example, but don't know which speaker is in which room because they all have the same name. If you're jailbroken, however, you can alter their names by editing a single file.
User hondavtec, on the iPhonewzealnd forums, explains:
Go to the following folder on your iPhone: "var/mobile/Library/Preferences" and copy the file "com.apple.MobileBluetooth.devices.plist" to your computer.
Open the file with Property List Editor, look for your specific device by opening the BT MAC address(es) and set a new device name under "Name" (not DefaultName).
Save the file and copy it back onto your iPhone overwriting the existing one. You might want to check the correct permissions (600) and then you NEED to reboot your iPhone!
That's all there is to it. While we don't know for sure, presumably these adjustments will survive an OS update (unless Apple resets this plist file each time, or you restore your device).
Rename connected bluetooth devices [iPhonewzealand]