Boot from EMMC and continue to use SD for storage

I solved this for myself and created an account so I could post it here.  I saw a few posts going back years which said either this can't be done on an Orange Pi 5 or they had no replies.  

The problem:

I wanted to boot my system from the EMMC but leave my large capacity SD card plugged in for extra storage.  The script in armbian-config worked as expected.  However, leaving the SD card inserted caused the board to continue to boot from it.  Wiping the SD prevented the board from booting at all.  I could eject the SD card, boot from the EMMC and then re-insert the SD card to use it as storage, but that's annoying.

The solution:

I noticed that the script in armbian-config left the boot partition on the SD card intact but removed the contents.  I used the following command to clone the updated EMMC boot partition back to the old boot partition on the SD card-

sudo cat /dev/mmcblk0p1 > /dev/mmcblk1p1

I then wiped the old root partition on the SD card like so-

sudo mkfs.btrfs -f /dev/mmcblk1p2
sudo btrfs filesystem label /dev/mmcblk1p2 SDcard

I rebooted and it worked!  I'll add /dev/mmcblk1p2 to fstab so it mounts at boot like a fixed drive. 

And I suppose future kernel updates will need to get pushed back to the SD card the same way (similar to updating your bootloader on a x86_64 system after a kernel upgrade).  Hopefully I remember this when the board won't boot after the next kernel update.  Slackware warns me to update my bootloader when slackpkg updates the kernel, but I know Ubuntu won't.  :-)