Like intelligence, personality seems to become relatively stable once one becomes an adult. So, like intelligence, personality (which I'm lumping compassion into) seems to emerge from a complex interaction of gene expression (nature) and environmental influences (nurture). So, again, I would argue that once one reaches adulthood -- mid-twenties -- the core of ones intelligence and personality are established.
However, there is research that indicates nature and nurture can both be trumped, to a certain, but powerful, extent by the mind:
The Social Life of Genes: Shaping Your Molecular Composition - Pacific Standard: The Science of Society
“You can’t change your genes. But if we’re even half right about all this, you can change the way your genes behave—which is almost the same thing. By adjusting your environment you can adjust your gene activity. That’s what we’re doing as we move through life. We’re constantly trying to hunt down that sweet spot between too much challenge and too little.
“That’s a really important part of this: To an extent that immunologists and psychologists rarely appreciate, we are architects of our own experience. Your subjective experience carries more power than your objective situation. If you feel like you’re alone even when you’re in a room filled with the people closest to you, you’re going to have problems. If you feel like you’re well supported even though there’s nobody else in sight; if you carry relationships in your head; if you come at the world with a sense that people care about you, that you’re valuable, that you’re okay; then your body is going to act as if you’re okay—even if you’re wrong about all that.”
So the fact that -- as willful entities -- we can cognitively shape our own "environment" is powerful. My only question is whether we can do so to the extent that we can significantly increase our intelligence or change our personality. If we can completely and radically change who we are, it begs the question:
who is changing
who?