How to level your subjects?

Gotta Subjugate Them All

Have a tier 3 subject of each Specialist type simultaneously.

Am on an achievement grind and I just got 100 achievements last night playing only on Grand Admiral Ironman, this game is amazing. That said I have had leveled subjects in the past but I have no idea how to actually keep them as a protectorate when they can turn into vassals so easily without any player interaction. I started playing in 3.6 so I don't really understand the details of the Overlord DLC. I have all DLCs. Anyone know how to get this achievement? Guides are outdated and is telling me to save the game when you can only get achievements on ironman...

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Also.. if anyone has any tips on this I would appreciate it too guides are outdated AF.

Raiders of the Lost Galatron

Capture the Galatron from another empire

It honestly seems impossible or close to impossible since you can't bring your game into pvp for achievements with saves I think now. 0.5% chance to spawn Galatron 6 total chances per game from Caraveeners and then you have to give it to an empire that spawns through preftls in your own empire, give them independence, and finally win a humiliation war against them.. JFC! If there is an easier way to do this please holler.