Additional action before existing action

How can one add an additional action before an existing action.

In the action editor, I select a shortcut with one assigned action, then click "Attach additional action". The additional action is added after the existing action.

How can I move the new action before the existing action, making it the first action for the shortcut?

That is currently not possible unfortunately. It will become possible with the big UI update (New BetterTouchTool UI Progress)