Conflicting Succession Law Conditions
Solution 1:
The second "One of these must be true:" is a parallel condition to the holding a viceroyalty condition. I'm guessing this is a mod, as usually the conditions wouldn't just be blank like that, but basically you'd be able to change the succession law because you fulfilled the second condition (currently blank) of the "One of these must be true". The reason you can't change it right now is actually just that second condition of "You must have ruled for at least ten years"