Is it possible to upgrade tribal holdings of vassals?

I am a new player of CK2 (current patch) playing as the feudal King of Sweden on the standard start date. I conquered some tribal holdings in the North via holy war and, noticing the 'wrong type of holding' penalty, granted these to some of my middle sons and other relatives.

These tribal vassals now hold a negative opinion of me due to 'wrong government type' and contribute minimal levies to me due to the tribal vs. feudal mechanics. I have since figured out the 'upgrade tribal holdings to castles' decision that can be implemented after upgrading hillforts to level 4 and now try to do this for any new tribes I conquer before giving them away.

My question is, if I upgrade my existing tribal vassals' hillforts to level 4 for them, will the 'upgrade tribal holdings' decision upgrade these counties as well, or does it just work for my demesne holdings? This would erase the strong negative opinion modifier and grant me actual levies from these counties, so I think it's worth the expense if possible.

crusader-kings-2

Pictures about "Is it possible to upgrade tribal holdings of vassals?"

Is it possible to upgrade tribal holdings of vassals? - A Woman and a Girl with Red Spots on Cheeks Holding Bowls of Milk

Is it possible to upgrade tribal holdings of vassals? - Photo of Women Standing While Smiling

Is it possible to upgrade tribal holdings of vassals? - Portrait of a Woman Wearing Traditional Clothes

How do you convert tribal vassals?

Adopting feudalismEditYour tribal vassals will be able to join you in feudalism as long as they follow an organized religion. Vassals are now required to construct a Stone Hillfort to take the decision. All tribal vassals are more likely to adopt feudalism if they share your religion and culture.

How do you convert tribal holdings to feudalism ck3?

How to change from Tribal to Feudal government in Crusader Kings 3

You have the Law Absolute Tribal Authority.

Your religion is an Organized Faith.

Your level of fame is Distinguished (Level 2) or above.

The Development level in your capital county is greater or equal to 10.

Have all Tribal Era Innovations.

How do you convert tribal holding to feudalism?

Tribal vassals do it on their own via the decision "adopt feudal ways via liege" for 250 prestige. If you have a tribal holding as a feudal, you can feudalize it in the holding interface (where you'd be building temples for example) for 500 gold.

How to Manage Your Vassals, Council, \u0026 Court in Crusader Kings 3

Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.

Images: Vincent Tan, cottonbro, Ganta Srinivas, Ganta Srinivas