I hate to be the bearer of bad news yet again (though last time it ended well), but we have official word now that neither yaks nor mushan were intended to be tameable.

Much like porcupines and silkworms last time, the tameables are the result of them changing beasts around in zones. Beasts that used to be goats or crocs were turned into yaks and mushan but the tameable flag wasn't removed before the build was released.
Of course last time it ended well, but I don't dare hope we'll get lucky twice. Personally I wish these accidentals had occurred first, as if GC was going to change his mind on two pets then mushan and yaks would probably make more sensible pets than silkworms and porcupines (though maybe not as amusing). Not that I'm complaining about those

Anyway, I just wanted to let people know now so they don't get *too* attached to these new pets. Maybe GC will show mercy once again, but I'm not going to get my heart set on it.