With me, absolutely no control - although my personality has changed. I used to be full of passion and loved to get involved; now I'm somehow arrogant and apathetic at the same time (I know they conflict).
For example, I used to be quite liberal, but now I disagree with quite a lot of liberal (and conservative) ideas. When I was liberal I used to get into heated debates and argue my position. Now I just don't care, I will say what I think but I wont get into a debate (It's often a waste of energy unless the other person has a really good point).
As you can guess this does not do me any favours when talking to new people. I genuinely do want people to like me though, so I try not to come across as arrogant or apathetic. This is more easily said than done, I always seem to revert back no matter how interested and engaging I try to be. I suppose I can't keep it up because I know that it's not how I am.
So to sum things up my personality changes naturally, but I have no chance if I want to change it by design.