Can I set the Crown Laws in other parts of my realm?

I'm the King of both Ireland and Wales and Crown Authority is High. I had vassals in Andalusia, but somehow I lost them to Scotland during a succession. I thought, isn't High Crown Authority supposed to prevent titles from leaving the realm through succession? So what I realised is that the succession laws of my vassals in Andalusia was under the de jure crown laws of a Muslim ruler who held the title of Andalusia, despite them being my vassals.

I'm having similar problems in Wales now where the successions are not going how I expect them to because they're not operating under the supposed Crown Laws of my realm. I'm in the process of invading England now so I can create the Kingdom of England, but now I'm wondering what can of worms I'm opening.

Does changing succession laws simply not effect vassals at all? I'm under the impression that all my titles will go to my heir, but do I have to worry about the Kingdom of Wales (or the future Kingdom of England) going to someone else because of succession laws for those de jure kingdoms that I can't control? If I later change to elective, will only my Irish titles go to my elected heir and the rest will go to my first-born heir?

Can I only set the crown laws for my primary title, or can I set the crown laws in the rest of my realm and titles?

Solution 1:

Succession laws for multiple kingdoms (and no emperor title)
(For your example where you are the King of Ireland and Wales)

1. King of Ireland and your lower titles that are de jure part of Ireland are governed by the succession laws for "King of Ireland".
2. King of Wales and your lower titles that are de jure part of Wales are governed by the succession laws for "King of Wales".
3. [Duke and lower] titles that are not de jure part of any of your King titles are governed by the succession laws for your primary title

Changing a succession law
If you changed the succession law for King of Ireland, and King of Ireland is your primary title, all of your de jure Irish titles and titles outside any of your de jure kingdoms (#1 and #3 above) will be governed by the new succession law.

You would need to change King of Wales separately. (In the law interface, click on the coat of arms for Wales.)

Succession laws for titles held by vassals
Your vassals have their own separate laws for succession which could be totally different from yours. For example, you have have agnatic primogeniture as your kingdom succession law, and your vassal duke could have agnatic-cognatic gavelkind as his succession law.

Solution 2:

Crown Laws are governed not just by Crown Authority but also by de jure Kingdoms. Vassals that are in another de jure kingdom get their crown laws from that kingdom, not from you. This can be remedied via assimilation but this has some specific conditions, namely:

• The entire duchy is within the realm of the king.
• The king does not hold the crown of the current de jure kingdom to which the duchy belongs.
• The ducal title either does not exist or is held by a vassal of the king.

After a year, you begin to see the duchy shaded as your kingdom. Then you can check to see how long it will take to fully assimilate that duchy by hovering the cursor over said duchy.

If you are an emperor, you can assimilate whole kingdoms in the same fashion.