I created an "Action" which has a method that reads:
Does anyone know how to modify an "Extended Property"?
Your method code looks like it's on the right track. What issue are you having? You haven't mentioned how your action is configured, so if you aren't seeing the action in your ui I would go to an ItemType you want to be able to use this with and add your new action to the list of Actions for the itemtype. (Actions relationship tab, select button, then search for the new action by name.) If you've gone that far, you should at least get an error with a bit more information.
The action is configuration is fine. It doesn't work with the "extended classification" property. If I add (this.setProperty("name","test");) to the method, the name changes to "test', but the extended property still doesn't change. I get no error messages. I'm not sure if extended classifications are handled different. TY
Ah, I believe you might need to add a line.
The SetPropertyAttribute function is used to create the property tag in the event that one doesn't already exist; given xProperties unusual relationship with items, this can be needed to properly function. Let me know if that helps.