...considered very bad form to ask for diversion around TS, and request would be refused. Is this still the case? Is there any history of an emergency declaration and diversion without clearance?
I don't know about "considered very bad form", but clearances to divert around weather are often not available from civil controllers in China due to the proximity of military airspace. The best way to obtain a clearance in such circumstances is to declare an emergency. That gives the civil controllers more ammunition to obtain a clearance from their military counterparts. You have to plan ahead and allow enough time, but the clearance is usually forthcoming.