You can change the text that is sent by modifying the language file in 'Program Files\Messenger Plus! Live\Languages\Lng_<language>.ini'
Do a search for "MenuSoundCommands=" and you should see the associated messages. You will need to restart Messenger for any changes to take effect.
You can also change the text that is sent on a per-use basis by simply typing after the sound's /s command, eg:
code:
/shello Hi!