Bit late for all that, Germany had already picked a side and it was Japan. Shipments of arms to China were banned in April '38 and Von Faulken and the military mission were withdrawn by June '38.Germany could even use the Japanese relations with Poland as a partial pretext depending on how the dice fall, and how much the Germans want to back Chiang Kai Shek.
We might not see too much German help to China, of course; the British should be kept occupied as long as possible from a German perspective. But the Germans over in China will do their utmost to help Chiang regardless of orders. They'd taken a liking to Chiang, and vice versa. Hitler might need to replace some of them. Still, selling arms to China might prevent the German economy from imploding slightly longer.
I suppose Germany could do a sudden pivot back again (it's not like this was a matter of deep ideology for them) but would anyone in China trust them? And without the infrastructure and personnel in place could Germany even do anything particularly useful anyway?