Imperial Succession issue
Ok so I created the Empire of Hispania in the year 1207. It was created with Agnatic Gavelkind laws, and so I waited 10 years to 1217 in order to change the law. I usurped the title King of Mauretania 3 years earlier in 1204.
For some reason I can't change the succession law to Elective even though I have ruled as emperor for 10 years (now a few weeks past the date I claimed the title), am at peace, have no internal wars going on, everyone has a positive opinion of me, and am not in a regency.
I can't change the laws for Mauretania either, even though I had the title 3 years earlier. So basically I am stuck without being able to change succession laws and getting stuck with a son I don't want as my heir.
Can anyone explain this? I have agnatic-cognatic elective set up in all of my other main titles (King of Leon, Galicia, Portugal and Navarra).