The presence of American troops just by bordering a nation will cause concern for Beijing. It will be a problem between Sino-American relations. Just like in OTL when the U.S. has actually surrounded China from the First Island Chain and even in Central Asia when there were U.S. troops in Afghanistan, Uzbekistan, and Kyrgyzstan during the War on Terror.What about unified Korea's relation with China? Would they still harbor American troops?
If so, this would probably make Beining more catious, butterflying the HK crackdown.
It probably may butterfly the HK crackdown since the POD is 1990s and the crackdown only occurred in 2019.