While I personally agree that "personality can and does change" and that such changes have the potential to trump so-called "external" factors, the research cited in this article doesn't seem to pack much of a punch.
Furthermore, I think that there are some major obstacles in the way of this kind of research in general. The average person's concept of what shapes one's personality is still heavily influenced by poorly understood notions of genetic determinism, philosophically naive definitions of free-will, and lingering ideas about human beings possessing a "soul" (even if such ideas are subconscious or secularly re-imagined).
Until there is a significant paradigm shift in those respects, I don't think we'll see the support or funding necessary to produce studies that yield actionable data.
‘Is Personality Fixed? Personality Changes as Much as “Variable” Economic Factors and More Strongly Predicts Changes to Life Satisfaction,’ published in Social Indicators Research (doi: 10.1007/s11205-012-0006-z)
[...] small positive personality changes may lead to greater increases in happiness than earning more money, marrying, or gaining employment.
[...]
We found that our personalities can and do change over time – something that was considered improbable until now – and that these personality changes are strongly related to changes in our wellbeing.
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Previous studies have shown that personality accounts for up to 35% of individual differences in life satisfaction, compared to just 4% for income, 4% for employment status and between 1% and 4% for marital status. However, because it was believed our personalities were fixed, policies to improve wellbeing have focused on these lower-impacting external factors.
[...]
“Fostering the conditions where personality growth occurs – such as through positive schooling, communities, and parenting - may be a more effective way of improving national wellbeing than GDP growth.”
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Personality was measured using a well-validated personality questionnaire assessing five broad dimensions which cover the breadth of a person’s personality: openness-to-experiences, conscientiousness, extroversion, agreeableness and neuroticism. The researchers then looked at the extent to which personality changed and how these changes related to life satisfaction in comparison to external factors, such as changes to income, changes to employment and changes to marital status. They found that personality changes at least as much as these external factors and predicted about twice as much of changes to life satisfaction over the study period.
Link: manchester.ac.uk/aboutus/news/display/?id=8035