At the startup screen, while the letters that form the Sga logo are moving around, press down several times. The word 'exellent' will then appear. You must start a new game to use this mode.
Enter a name for the main character, then put the cursor on ''END'' hold the Start button and press 2. Prince Nick will appear; give him a new name, then put the cursor on ''END'' hold Start and press 2 agine to access menus that will let you rename all the characters.