A survey to the readers on how the contact with the Westerosis should be made.
As I see it, I think it is necessary to have a deal with the old elite so that the Prussians can rule with some kind of stability and not have to endure rebellion after rebellion due to cultural and religious problems and the intervention of other nobles.
The other thing would be to change the beginning of the story a bit and have it appear in the reach and with a bigger army than it was in the first time, since it would be the only way to guarantee a decent control without depending on the help of the old elite, besides having a rare peace with the seven kingdoms while they heal from the civil war, this would be the path of conquest and would have to change everything I have written it would be completely new chapters, and they would be quite similar to what lothar did in essos.
Although clearly with more direct control from the MC to the overly fanatical actions that would turn the new subjects against him.