Secrets and Lies is a little inaccurate when it implies that only the third form of Occlumency changes your personality. In fact, all three do: the first one (Dumbledore, Voldemort, Snape, Hermione) tends to make you colder and more calculating, the second (Harry) tends to make you more temperamental, and the third (Luna) tends to make you more prone to dissociation. There is no good way to practice Occlumency—restructuring your mind in order to shield your thoughts is fundamentally detrimental to your mental health.