End the Manchu Dominance is a decision unique to 
China.
It requires that China is not civilized (and technically not a great power either although that is not possible when it's not civilized) and that the year is after 1860.
It is allowed when the average consciousness is at least 3.0.
It gives 0.1 years worth of research points. Additionally all Manchu POPs gains 2 militancy and 1 consciousness.
The research points will help china westernize although 0.1 years (around 35 days) of research points is not a lot. The extra consciousness and militancy might be a problem, but Manchu only make out a tiny proportion of the population, way less than 1%, since the substate 
Manchuria is most likely not annexed yet and they hold most of the Manchu Pop.
In the game files it is called 'Clear out the Manchu Elite instead