As the title says above, the challenge is the Vietnamese Muslim Dynasty with POD before 1900.
What'll happen if the Vietnamese (or Champa) Muslims ascended as the ruling Emperors of Vietnam? How would it affect Asian geopolitics as of result?
Bonus points if their territories encompassed whole of Modern Vietnam.
So, you probably need a PoD before 1475, when the emperor Lé Thai Ton wiped the floor with the Champa.
What you could see is, at the end of the Tran dynasty, either Ho Qui Ly or one of the Tran emperor (but how much agency did they still have?) agree to a marriage with a Champa king/prince to bring peace and power and stop the constant aggression.
Question here is, how desirable would that be for the Champa? Raiding Vietnam is a great source of wealth and prestige (which is why they kept doing it through the XVth century despite being repeatedly bashed on the head as a response).
At any moment of war/tension with China, it becomes much more complicated because Champa was a tributary of China and often used as a counterweight, an advanced base of Chinese power against the Viets. The Champa even went so far as to request formal annexation by the Chinese! (Can't remember the year though, I'd say Lé Than Ton period).
After Lé Than Ton destroyed them, you might still have marriages/alliances with remaining Champa princes, but then there wouldn't be enough in there to get the dynasty to convert to another religion, given the emperor was depositary and symbol of the local religion (some kind of buddhism).
I would go with a Tran Emperor trying to avoid Ho Qui Ly coup by marrying a Champa prince to evict him. Tough but possible. Or a Tran led coup against Lé Loi after the peace of 1427, but also tough to pull off given popular support for Lé Loi.