You cannot hack the mainframe to change your grades (probably), but you can manipulate the XP multiplier.
Because V0.331 has a secret patch note: "Every failed quiz is just a respawn point. Every bad grade is a tutorial level you skipped." High School Master Cheat Code Cheats - V0.331
Here are some additional tips and tricks to help you get the most out of High School Master: You cannot hack the mainframe to change your
that a transparent input line or drop-down box displays in the top-left area of your interface. Active Resource and Stat Modification Codes High School Master Cheat Code Cheats - V0.331