Start your Superstar with 99 in ratings in Superstar mode
Go into the Superstar Hall Of Fame and choose a player based on which position you would like to play through, appearance, etc. At this point you are not selecting them, but you know which player to alter. Go into Roster mode, to the players' team, and start alteration. You can change all the characteristics that let you highlight them as usual. Once you have changed the appearance, etc. go to ratings and adjust them as desired. Go back into Superstar mode and the player you modified will be at the top (if you made them with perfect ratings).
Go to the rosters and look for a player that is a rookie at your position. Alter that player as desired (appearance, build, etc.), then change the ratings to suit your taste. If needed, trade that player to your favorite team. When leaving rosters the game will save. Then, start Superstar mode and select "Rookie from 07 class". Be aware that this player's ratings will apply to other game modes. Select your player and continue.