Yes and no.
I've always been kind of an emotional person, but more than anything else, I calmed down after I transitioned, because I was finally taking care of what caused me so much anguish. I went full time in late 2000, and I remember commenting to a coworker in 2001, that it almost seemed to me, like I was a different person. She agreed with me. When I asked her what she saw in me, that made me seem different, she told me that before I transitioned, I basically behaved in one of two ways, I was either angry, or I was sad (which makes sense, since I was a complete and utter mess by the time, I got in touch with an area gender program in late 1998 - you most assuredly did NOT want to be around me, because I was a very unpleasant person [I had reached a point where I was contemplating suicide, if I didn't do something to start transitioning in the near future]). There was no generally happy or content state for me. My coworker told me that after I transitioned, I looked so much happier (especially with myself), and calmer (things didn't set me off anywhere near as much as they had before), and that transitioning had been a good thing for me to do.
I think that for many of us, a lot of the personality changes come from the calming effect that occurs, when we finally deal with the anguish that gender dysphoria causes us.
Ellen
HRT - 1999
Orchiectomy - 2001
SRS (Yeah!!!) - 2003 by Suporn