For the "fieldpromotion" code, which gives you 100 experience points, you 
can input a ; after the word and repeat the cheat. For example, enter 
2fieldpromotion;fieldpromotion;fieldpromotion;fieldpromotion;fieldpromotion;".
You can continue this up to eight times per entry. So instead of 100 experience
points, you will end up with 800 every time you press [Enter]. 
Note: This should be possible with other codes as well.