This is where true roleplaying begins. Learning to truly roleplay means to let go of the personalities and identities we see as ourselves and becoming someone else. If you can engage your child personality fully in the act of play and embrace your character, you are in a very real way, consciously choosing an incarnation in which to learn karma and life lessons that you as an individual are resistant to learning.
This tool works best when you are a fully engaged player and are blessed with a fully engaged storyteller and rp group. As with thought forms, astral constructs, and other "advanced" forms of magical creation, group effort produces the most intense effects. There are a couple of reasons for this. From a magical perspective - more people = more energy = more "concrete" construction. Society is an excellent example of this principle at work. From a scientific perspective, there is a point of mathematical "critical mass" that defines the point at which reality is altered by the belief of people. This number is always the same in relation to the population at large. Thus, when a small group of people are present, their collective belief system alters their immediate reality. Ergo, get a bunch of people together who create a communal reality - and you wind up with a very complicated, intricate, and large world (or worlds) - that is also very REAL.
Another means of allowing roleplaying to work most effectively for you is to grow to the point of creating a character who seems least like yourself. This allows for surprisingly new perspectives on life - and profound spiritual realizations. My admittedly favourite character at present is one that I still marvel at playing. She is many things I thought I would never play - but I have learned incredible life lessons from her. As my spiritual journey informed the perspectives from which I approached her life trauma - her amazing growth in response (which also makes her the thing I never thought I would do) has informed my spiritual growth in return - intertwining our karma. This is due to the degree to which I have allowed myself to step outside of who I am and what I do - and experience situations from radically new perspectives. In playing her I allow myself to fully experience "crazy" - which is perhaps her ultimate gift to me in terms of mental shift. By completely shedding myself of cultural boundaries and definitions and disregarding the concept of "crazy" I have found the freedom of my authentic self.
So how do you reach the point where your roleplaying character teaches you karmic lessons that you were ignoring for years? Play. Play. Play. Play until you fall back into make believe again - and find a troupe of friends who make believe with you. Better yet, find a game everyone enjoys, and bring your whole spiritual group into it. Incarnating as alternative selves with the people you attend ritual with speeds your development as a group - and alters social relationships to the point where people can more easily overcome shared karma and learn shared lessons. That is what breeds healthy and strong spiritual groups - and honestly, makes the most amazing games.
And then go lose yourself in someone you never once imagined yourself to be - and give yourself the freedom to change.