Most contemporary psychologists agree that there are 3 major factors determining human personality - these are 1) genes; 2) prenatal development; 3) early childhood.
My dream is inventing a way to set the necessary personality characteristics on the 2nd stage, since the rest stages are something we can hardly control. Most likely it's going to be hormonal additives to the food of future mother influencing the prenatal development of fetus.
This way you would be able to choose the nervous system type of your future child - what proportion of sanguinic, melancholic, phlegmatic and choleric traits you child should possess; whether he/she should be apparently feminine, apparently masculine or anrogynic etc.
Perhaps such technologies will be available one day. The main point is preventing all possible side-effects these hormones may have on the mother and the child.