It is not likely that anything, other than an official protest from China will result from placing a dozen or less Marine Guards at the brand new defacto Embassy in Taipei.
The same can be said for appointing a senior carrera Diplomat as head of the American Institute,who will be a defacto US Ambassador to a non-existing country. (Which US does not recognize as independent)
Why are they doing this, other than to piss of China? What are they hoping to gain by this action?? (If it happens)
I can see no gain from this but plenty of pitfalls:
It helps cementing support for the Chinese Government among its own people and by countries who also feel bullied by the present US administration. (There are plenty of those these days)
It gives China an opportunity to take the US to the Security Council to get a vote against. (Which will be vetoed)
It can stir up the pro-independence parties in Taiwan to believe that the US will actually come to their aid IF they should provoke China into changing status quo.
Another proof that the present US administration live in their own dream world, or in the wrong time.