If you are specifically trying to change your name for , there is sometimes a separate setting at the bottom of the LAN game lobby menu that allows you to set a custom display name independent of your main career profile.
Accept the default name "Player One" when first starting the game.
Mira’s eyes widened. “That’s insane. The physics engine updates at 600 Hz. The UI updates at 60 Hz. The overlap would only happen during specific physics events—like crossing a finish line, or hitting a curb, or… or a name-change event in the career mode.”