Will claiming the Mandate of Heaven break the Roman Hegemony?

Hello I found the Roman Hegemony starting as Dijon Ironman and expanded a whole lot into Asia and after Genghis Khan conquered China, I used Consolidate Land Under Heaven casus belli and boom I got all of China. Now there is a decision called Claim the Mandate of Heaven. This decision switches to Celestial government. My Government is administrative.

My questions are:

- Will I lose the Roman Hegemony and only be Hegemon of China or will I have both hegemonies?

- And if I switch to Celestial will I still be able to choose any child as my heir? Or use influence to make someone from another house in my dynasty the Hegemon?

-In general will I have any big challenges?