A Word of Warning:
This tool has it's name for a reason (and no, it won't make you / your 3DS invulnerable): It gives you power over the files and data on your NANDs like never before: You can do basically anything you want with that NAND. Needless to say, you need to use this power wisely. While GodMode9 itself is stable software, it won't protect you from yourself, and a full-brick could be just one bad decision away. There is a write permission system in place, but even that can be overridden by the user. While being thoroughly tested and in daily use by a growing number of users, I can also not fully exclude that there are some small bugs left. In short: I am not responsible for anything that goes wrong while you're using GodMode9.