I have noticed that several people have asked how to change the notification icon on mumbles without creating a new plugin.This is actually very simple: use the generic DBus plugin with dbus-send. I believe that this tutorial requires the SVN version but I may be mistaken. First add a new section to your DBus plugin configuration file. If you do not have this configuration file, copy the sample one from the mumbles source tarball (found on the project's homepage). The file is called dbus.conf.sample. Copy this file to ~/.mumbles/dbus.conf. The new section is as follows:

enabled = true
interface = org.program-or-script-name.DBus
path = /org/program-or-script-name/DBus
signal = your-signal
icon = your-icon.png

Put your-icon.png in the ~/.mumbles/plugins/icons/ folder.your-signal is your name for the alert. None of these variables are important but they must be consistent.

After doing the previous and restarting mumbles, run this command:

dbus-send /org/program-or-script-name/DBus org.`*program-or-script-name*`.DBus.your-signal string:"Title" string:"Message"

Make sure that you replace all necessary variables. This will display a mumbles popup with your custom icon, title, and message. You can also specify a click action using launch = action.