You will need to save the change to a global token that is set to
persist across launches.
Then on startup or resume, you need to get the value stored in the
token and apply it to the join.
You could store a heap of join values in one token, just use a
single object in JavaScript and convert it to JSON format saving the
token value, then convert it back when loading it.
CF.setToken (saving token values), CF.getJoin (loading tokens),
JSON.stringify, JSON.parse
CF.userMain, CF.watch with the GUIResumedEvent.
Those are the functions that you will need to make use of.
http://www.commandfusion.com/docs/scripting/