The "big five" has a useful benefit in creating a common vocabulary of complex ideas like intro/extroversion but it is a very broad organization system for these concepts. This is why even knowing your "type", as with the Meyers-briggs types, does not in itself lead to personality change; it is more about awareness. I like that you brought in the power of habit to the discussion. As a neuroscientist, neuroplasticity is my tool of choice for making "healthy" changes in personality that aim to achieve the highest forms of well-being, for each individual. Having the focus you reference, the willpower to continue progress toward goals, is essential and also trainable. Our personalities are our reactions to the circumstances of living, but often people are stuck in loops created by more primitive processes like flight or fight; setting concrete, specific goals and showing up every day can evolve our well-being.

Thanks for writing up on such an important topic; we all have the power to master our life, we just need to take responsibility and action! ;*