More checkmark options in the Tasks

We'd like the ability to have more options in the Tasks.  We use Service Catalogs for routine processes, like our new hire, terminations, employee changes, etc.  We created the form to cover our tasks that apply to the majority of our employees.  However, there some cases where those tasks don't apply.  It would be nice to have the option to EITHER check mark the item as DONE or Not Applicable (rather than checking it done and then going to comments stating it is not applicable).

We'd also like the ability to uncheck an item.  Sometimes things get checked accidentally and we can't undo it.