It's basically impossible to fully (software)brick a 2|3DS with B9S by accident. In 99% you will still be able to boot into GodMode9 even if the main operating system is fully trashed.
* Troubleshooting software damage is not always easy. Describe your problem as good as possible on the forum and chances are you will get competent help.
* Keep a NAND image in a secure location for the worst case (full NAND restore is not the first thing to try though)
* For ntrboot (needed if B9S has been overwritten) you will need any other DS system can flash ntrboothax on your flashcart like explained on the guide:
https://3ds.hacks.guide/ntrboot
You can ntrboot right into GodMode9 by providing it as boot.firm (instead of SafeB9Sinstaller)...