If we were going to engage in a long debate about this, we would first do well to define our terms: trait, characteristic, personality, behavior. I would not call frugality a personality characteristic, but rather a behavior, and indeed I would say that frugality is one of those things that is likely shaped by environment (as well as culturally defined).
But it seems self-evident to me that not all of our behaviors are that malleable. Otherwise, if as you say, being cheerful and upbeat gets a more favorable response, wouldn't we all be cheerful and upbeat all the time if we could?