I am doing a research and I am investigating if personality based instructions improve the performance of athletes. Please name some titles of papers about the topic.
Generally it is very unlikely that personality traits can be modified. But in specific situations some traits might be adjusted. This article could work for your research:
Querstret, D., & Robinson, O. C. (2013). Person, Persona, and Personality Modification: An In-Depth Qualitative Exploration of Quantitative Findings. Qualitative Research in Psychology, 10(2), 140-159.
It depends on what personality traits are. Generally, of course,they can be changed. All the therapy aims to change it. For me, a behaviorist, it is very clear, A shy (stubborn) person goes to a behavioral or cognitive therapist, and after the training shyness (stubborness) disappears.
As Vladimir says, it depends on what you consider traits to be. If you adhere to the OCEAN model (McCrae & Costa), then they are pretty much biological and hard-wired features.
An interesting direction is to understand how we can use the personality of the athlete to enhance her or his performance. I research on Motor Imagery, and I think this article might interest you
It shows that, when given a self-enhancing opportunity, narcissists benefit more from an External Imagery Perspective (or 3rd person) rather than an Internal Imagery Perspective (or 1st).
Yes, all depends on definition. I am not directly in the field but I am asking myself whether these traits you can change are more situation specific. I can probably give a therapy to change shyness in specific situations, but this does not necessarily mean I change the manifest trait.
To confuse Ahmadreza a little bit more, here is the article about the heritability of Big Five traits.
Bouchard, T. J. and McGue, M. (2003), Genetic and environmental influences on human psychological differences. J. Neurobiol., 54: 4–45. doi: 10.1002/neu.10160
Matteo is absolutely right, try to find some ways to use your knowledge about personlity to improve results of sportsmen.
So, you can change the personality, but to some extent. And remember that the old traits can express themselves in an extreme situation. For example, you have a shy coward, you train him to be a good soldier, but in a war he suddenly deserts because the fear and stress make his new traits (valour) disappear. I think it is what Andre speaks about.