Being able to change the Sims demeanor

i wish EA would make it possible to change the demeanor of our Sim characters 'cause sometimes ill make a character and i want them to act more calm and collected or more mature and elegant, but then i watch my Sims and they're always a bit goofy and really joyful (which i dont hate, it just sometimes doesnt match what i have in mind for when i make a character with a certain personality i have in mind.) PLEASE EA!! HEAR MY PLEA AND MAKE THIS A POSSIBILITYYYYYYYYYYY!!!!!!!!