I was able to make this work using NodeRed without a script or invoking dbus. The key was to setup the Digital Input in the Cerbo GX for all the values (including custom name) to appear properly in NodeRED.
First, as noted above use the Victron Custom Control.
In the custom control you select under the “Custom” dropdown “com.victronenergy.settings” then “/Settings/DigitalInput/1/AlarmSetting” under the next dropdown.
You then need to send a value of “1” to the node on “msg.paylod”.
From there you create another Custom Control to send the text for the alarm. In that node you select your Digital Input you are using for this. Keep in mind it will be the custom name you choose in the Cerbo GX UI, but it will also change to show the last alarm message you sent. Again, I sent the alarm message on msg.payload.
One observation, once the alarm is sent it will not send it again even if cleared. To make that work I had to reset the Alarm Setting back to “0” .