Add Additional Action using JavaScript

Is there any way to add additional actions in JS?

I'm trying to use the setAction() method to add an additional action to a form created in InDesign. It already has nearly 100 show/hide actions that were set up in the InDesign document. When I try to add a JS action on mouse up using the setAction() method, it deletes all of the other actions instead of adding to. There wasn't previously a JS action on the button I'm trying to add it to, only show/hide fields.

Any ideas?

I've been trying to create a workaround by using the visibility of a checkbox as a trigger without success...