Can practice of pranayama change mental traits of a person?

What are the psychological effects of pranayama/yoga/meditation on mind other than relaxation and body building? some claim that these increase creativity. How is that possible? some say that these teach one to live life as a spectator rather than as a participator. How can that be helpful in practical life? Does determination, tenacity, ambition, drive etc increase/change if one practise these? anxiety and stress are due to external factors and should one not try to reduce these by rational thinking rather than doing pranayama?