As I said before most airline in China are owned by government and if need be they will be told to buy Chinese product period
Nope, it doesn't work this way. Unless you want them thrown off market, off course.
1.You may "ask" them, but product(whole product, not just the plane itself) will have to be competitive enough across the board. Because "asked"company is an enterprise, it actually can be somewhat patriotic in its choice, it can be threatened and/or rewarded, but all this to certain degree.
First and foremost - air transportation is just wealthier business than aircraft production.
At worst, you'll get situation when your liners will be considered as a national "bribe": buy some of this stuff to operate unhindered, and park them somewhere.
2.Such overconcentration on "closed" home market is deadly in its own right.
Above Russian liners were remembered. Yes, there were a lot of reasons they were so unsuccessful after the fall, primarily the very disintegration of SU itself.
But there were others(reasons), and many of them closely related to wishes of one main "customer". Ssy, it was
Aeroflot, which specifically asked for 3rd crew position on tu-204 and not Tupolev.