I already do this myself, but it makes sense for everybody. When launching from an NTRBoot card, if it loads SafeB9SInstaller as ntrboot.firm, then you don't need to remove the SD card more than once. The current guide has the b9s install, followed by removing the card to replace boot.firm with Luma. Instead, you should have both Luma as boot.firm and safeb9sinstaller as ntrboot.firm.
EDIT: I'd make a pull request, but I honestly don't know to do it properly (ie. only have boot9strap_ntr.firm look for ntrboot.firm, while boot9strap.firm looks for boot.firm) so I just built it once normally, then made the change and made a clean build to use the ntr.firm for flashing to the flashcart.
I already do this myself, but it makes sense for everybody. When launching from an NTRBoot card, if it loads SafeB9SInstaller as ntrboot.firm, then you don't need to remove the SD card more than once. The current guide has the b9s install, followed by removing the card to replace boot.firm with Luma. Instead, you should have both Luma as boot.firm and safeb9sinstaller as ntrboot.firm.
EDIT: I'd make a pull request, but I honestly don't know to do it properly (ie. only have boot9strap_ntr.firm look for ntrboot.firm, while boot9strap.firm looks for boot.firm) so I just built it once normally, then made the change and made a clean build to use the ntr.firm for flashing to the flashcart.