I am using a custom action, Call function from attached native DLL. In the Properties section, there is an Edit... button. When this is clicked, an Edit Custom Action Parameters dialog appears. I insert a reference to an installation file, and the change appears in the Function: field. Since this field is normally populated by using the drop-down list, it would make more sense for the Edit... button to affect the Action data: field, even though it is currently positioned by the Function: field
Indeed, it would make more sense to have the Edit for the Action Data field from the custom action properties. A fix will be available in a future version of Advanced Installer, thank you for bringing it to our attention.
If there is anything else I can help you with, please let me know.