Later I found out that actually the device converts the selected ringtone to a mono .wav file. (And it also does that quite buggyly. ) Look at "/home/user/.local/share/sounds". So, a work-around would be the followig: The same daemon described in my above post, but instead of manipulating the config, it should also convert the personal ringtones to .wav, and then simply rename the files before the phone application plays them.