Mandala & China question

Hi,

after playing around in China and Angkor for a tiny bit I'm contemplating a longer run.

However, do I understand correctly that claiming Hegemon of China will remove all my cool Mandala stuff, like the Temple and everything and I basically become Feudal with special subjects?

And also: how do I turn my realm into a Mandala realm (assuming I'm something like Haesteinn coming to the area)?