You can access the cheat code menu by going to "My WWE", then "Options". "Cheat Codes" is an option there.
These superstars can be unlocked by completing WWE Universe One-on-One matches (Select match and One-Player only); they can also be unlocked via Road to Wrestlemania, in certain stipulations.
This only works, when you playthrough the Road to Wrestlemania with Christian.At Elimination Chamber PPV, talk to Edge about the time machine. Next, go to the GM Office and talk to Mr. McMahon, and he'll tell you that it's broke into three pieces. After you talk to him, there's action figures of Edge and Christian, located between the bookshelf and the TV. After that, leave and you'll get a phone call from Edge. Afterwards, you grab the flux capacitor in the Green Room and the phone booth in the parking lot. After you grab all three itmes, return to Edge and he'll build the time machine for you.When you do, you'll be able to go back or forward in time, to the completed events in your Road to Wrestlemania with ANY superstar's storyline.
As you play WWE Universe, you can unlock different venues to play in Exhibition Mode; only one Arena can be unlocked in RTWM.(NOTE: Wrestlemania, RAW, SmackDown, Superstars, Royal Rumble, SummerSlam, and Elimination Chamber are already available by default)