Changing existing Game Genie's NES codes
First, if the code you want to change contains eight letters, you will have to get rid of two of them. Use the table from the codebook:
A P Z L G I T Y
E O X U K S V N
Start by finding the third letter in the bottom row, moving up to the letter immediately above it, and replacing the third letter with that letter. Next, find the sixth letter in the table and move up or down so that it is in the same row as the eighth letter. Replace the sixth letter with the new letter if it is not the same, then drop the last two letters. For example, TOULETTS becomes TOLLEV. PIKKYPIG becomes PIGKYP. You may wish to enter the truncated code to make sure it still works. Note, however, that many codes acquire side-effects when shortened, some crashing the game.
You can change any part of the code you wish. However, some changes are less drastic than others. Making small changes to the code results in a new code with a similar effect, or one that affects the same area of the game. Larger changes create radically different results. The following list sorts each character slot from largest change to smallest change:
4 6 3 5
Slots 1 and 2 are not listed because they do not truly change the code. Slots 7 and 8 are not listed because they should never be changed and indeed should be removed from the code as described above.
When using the above list as a guide, the letter in any given slot should be changed to another character from the same row of the character table at top. If the fifth letter is an L, for example, you could change it to Z or G, but not X or K. It is legal to change a letter into the one opposite it in the character table. By this method, however, each slot makes a differently-sized change to the code than before. From largest change to smallest:
5 2 4
Again, slots not listed do not change the code significantly. Using this method, if the second letter is T, you would change it to V. This method produces larger changes in codes than the previous one.
