Yeah I don't think you can without creating a new account or something but I could be wrong. I was just j/k you may not want to lose your senior statues on Stangnet by changing your user name. But if you do just come up with something without the year of the car or you may have to change it again if you get a different Mustang LOL
Anyways, there is nothing wrong with remembering were you first started. My first car was a Ford Escort LX (I loved that car ohhhhh the memories) LOL Then I bought my 1987 Mustang GT hey so we have something in common