OK, so I decided to give it a try myself. I used ntrboot_flasher.firm to turn my flashcart into an NTRBoot card. The backing up and flashing process were both successful, but there wasn't any way to try it because I didn't have any unhacked systems handy (they were all hacked with boot9strap). So I tried to flash it back to its original state. No bricking happened, and it works once again as the flashcart it was before. In short, while I can't confirm that it works as an NTRBoot card, at least I can confirm that flashing it back resulted in no brick.