It kind of sounds like you want to make a "Custom View". A Custom View takes the base original 1040 View and adds or remove columns from it. You can do that by clicking the gear icon in the top left of the homebase grid. 

Here's a video: How to Create and Edit a Custom View 

So the answer to your question is: You cannot add to a regular formset view. You must create a custom view. If your formset view is missing columns or you want to reset the view to the way it looked originally just go to the top Homebase -> Reset View