I have kept an eye out for Conscientiousness interventions for the past 2 or 3 years, searched on occasion, and have seen nothing ever suggested except possibly stimulants like amphetamines. Possible instances like military experience generally turn out to be selection effects. As well, the Duckworth paper linked in the sibling comment, extensively discusses the numerous correlates and versions of Conscientiousness before adulthood stretching all the way back to early infancy.
So, as much as I'd like there to be some easy environmental intervention to boost my own Conscientiousness, I haven't found any.
Given the research that you cited, I have updated my probability estimate – that Conscientiousness is indeed rigid, higher from my original estimate of 75%. Wikipedia provides very accommodating definitions of Conscientiousness, inclusive of many behaviors such as being efficient and systematic, elements such as self-discipline and thoroughness, aspects of industriousness such as productivity and work ethic, and finally a strong association with procrastination.
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