Does anyone have a unused swap it shop code?

Its kinda weird that you ask that, because my friend told me how to use an old one. This does not always work, but if you try again and again, it probably will. Look at the last letter of an old code. If it is an A, change it to a B. If it is a one, change it to a two. Get it? Another example: d=f 9=1. If it is a 9 or a z, change it to a 1 or a A. Keep on going to the next character. If all do not work, you need a new code, or try it with the second to last character.