To what extent can we shape a child’s personality?

We can do it to such an extent as we know how to do it properly.
Assuming a child is normal, without any impairment of his brain, the limit of his capacity and intelligence is the intelligence of the trainer. To do this task it would be needed some intuitive feeling of what is correct or not in the training or educating a child.
Just think about teaching a child to play the piano. There are thousands of children out there, in western countries and in China, learning to play the piano. They are better and better each year. In China because it had become very popular among the middle classes to have a child that plays the piano, they had put 3 factories to make pianos. Most of the western piano makers, are working now mostly to export pianos to China.
What I pretend to say with this argument of the piano is… that it is not enough to play well the piano, for there would exist thousands of young people in ten or twenty years able to play very well the piano. The problem is there will not be enough people ready to pay for hearing them to play.
The same can be said in general, about academic intelligence. Any intelligent child must the best of the planet, or close to. For intelligent children had become quite abundant nowadays.
If you have some doubts, read about the Flynn effect.
Human Intelligence: The Flynn Effect | James Flynn and Stefan Molyneux
This matter is controversial, for it goes against the dogma that the intelligence is genetic. If you dismount or assume that intelligence is a learning process, similar to learning piano playing, there is not any controversy any more. Nobody can learn to play the piano unless it is well trained to do it.
The same is intelligence. Intelligence refers basically to language, and our capacity to discern about logic or illogic speeches. It can refer to our capacity to analyze and understand certain topics of maths, physics, etc. In general, about sciences. It is about logic, and logic comes from “logos” the Greek word for a speech. Politicians in ancient Greece had to be able to make good speeches when they wanted people to accept the next war, by example. Then, logic is mostly about appearances of something that look rational and believable. Then, this is a tricky question. Many of our rational assumptions are crap.
Of course, this idea can be thrown back at me, on my argument that intelligence is a learning process. Many people is maintaining intelligence is genetic, or at least half and half. Half learned, half genetic.
GIFTED 4 Year Old Boy Plays Piano like a PRO
It is easy to find this is wrong with the case of the piano. How can playing the piano be half genetic? Genetics is something very old. Which was the mechanism by which some humans had acquired some favorable genes to play the piano, or play basketball? If we put this idea over unusual behaviors, like to play chess, or to play tennis, the idea of some genes favoring this or that, looks preposterous.