China already declared that it will use force in Taiwan if "possibilities for a peaceful reunification should be completely exhausted". From Chinese Anti-Secession Law: Article 8: In the event that the "Taiwan independence" secessionist forces should act under any name or by any means to cause the fact of Taiwan's secession from China, or that major incidents entailing Taiwan's secession from China should occur, or t…
Chinese law should almost never be considered something that constrains the government, and especially not in grandiose cases like this. The government will do as it pleases, regardless of the law. That is more of a strong press release than a binding proposition. However, I am not arguing that China is not serious about retaking Taiwan. They are deathly serious.
wriggling around the law needs only an emergency.