I always execute an advanced actions for Pass/Fal actions, that will give you all possible statements (except Increment... because they are never available in advanced actions, one of the feature requests I have already entered several times). In this blog post I tried to explain the functionalities of question slides and the score slide, and those Pass/Fail actions are included in the blog post:
Enable and disable actions are greyed out if there are no suitable interactive objects (e.g. buttons or clickboxes) on screen that could be enabled or disabled by the action.
If you want to see Enable/Disable appear listed. Add a button to the stage, then try setting ON Slide Enter of that slide to Disable the button.