Agreed on principle. At first, this seems like a no-brainer: any attempt to separate Taiwan from China should be treated as an attack on Chinese sovereign territory.Stockpile a thousand DF-41 and DF-ZF and put it into public law that any attempts to separate Taiwan will result in nuclear confrontation. That should deter American adventurism.
China's stance is clear as it is but some people still imagine that China would not risk nuclear war over Taiwan. China just needs to make it more clear.
However, China's nuclear strategy is based on second strike. Changing that policy to have a first-strike condition will require substantial changes to China's nuclear capabilities.