Can you change the hair and eye colour of an existing Sim

buy the mirror and click on it
yes you can if you have a mirror
I don't think u can change the eye and other parts of the face til you reach a type of career reward
If you have Sims 2 university and get a job in the showbiz career a reward is the plastic surgery kit you should be able to change a Sims eye colour with it. Be careful when using it though.