I have a Pinebook Pro, but this probably applies to anyone with multiple kinds of storage. I would like to put Manjaro with an alternate window manager on an SD card and run it. Last time I tried, I managed to fry both installs. I seem to remember that there was something with partition naming that caused things to get improperly reused, and it could be resolved by changing…something. However, I can’t find where I saw it.
With 21.04 release and going forward, we now use PARTUUID’s in fstab and bootscripts, to make sure the wrong boot partition is not mounted.
If your install eMMC install is older than that, you can just put in the PARTUUID of BOOT_MNJRO to /etc/fstab instead of LABEL and the PARTUUID of ROOT_MNJRO into the bootscript of your device, instead of LABEL.
To find out the PARTUUID’s, you can run lsblk -o NAME,PARTUUID.