Root your device first.
Since iOS components can be propitiatory, I cannot explain what to do with that.
But let's say you have a tune called "YourTone" in any format( .mp3, .m4a...or any format. even a video file with the required sound) with you.
Convert the required notification to ".ogg" format. You can do this very easily via an online converter.
Then, send that "yourTone.ogg" file via bluetooth to the device.
Finally, using an app like root explorer, copy the file you just sent to your device to the "notifications" folder. Here is the full path to the "notifications" folder.
system > media > audio > notifications
Now, go to settings and you'll see your newly copied "YourTone" under notification list.

Enjoy.