Not for reference, just sharing my own case.
As I have a very low BW internet access so far, downloading JP or SDKM is a pain, so I just flashed a SD card with first L4T version having OTA upgrade support, then installed a 970 EvoPlus SSD into my B02 devkit with NX, created partitions with GPT (made 2 sibling partitions for backup), then cloned rootfs with rsync to NVME SSD, then edited extlinux.conf with a config booting Linux image (and DT if any) from current (emmc) boot, but with rootfs given as Linux boot args providing PARTUUID and adding initramfshooks such as (here from @crazy_yorick ).
Then rebooted my jetson with the new config from extlinux, then renamed /boot to /boot.archive, and made a symbolic link /boot to emmc partition /boot directory, so that l4t-bootloader updates are done in place. I just use /media/user link as this fits my case always logging in GUI, but if not this case, a proper mount from /etc/fstab should do it as well.
So far I’m running happy with this…I’m currently up-to-date running R32.5.1…as long as my NVME SSD is alive, because my SDcard may no longer be able to boot as I can’t keep my SD card up-to-date because of missing room.