You can practice being more extroverted until you get good at social interaction. I can context switch between the two (introvert / extrovert), but I would tend to think of myself as more innately an introvert in that I am quite happy on my own. The true extroverts seem to find being alone quite hard.
I suppose it's trainable as well. But your past is always a part of you; an extrovert who trained themselves to be comfortable alone may still think of themselves as "more innately an extrovert".
