Is there a way to update a Mac to High Sierra or Mojave if OEM SSD is unavailable? I have a late 2013 Mac Pro that had been running Sierra before its internal SSD died. I'd like to replace the internal drive, but OWC's site indicates the following:

"macOS 10.13 and later versions include an EFI (firmware) update that adds support for the Aura Pro X to the host computer. If you do not first update the host firmware by installing macOS 10.13 or later onto the existing SSD, the Aura Pro X will not function properly once installed."

Is there a way to get the Mac's EFI updated using an external drive so it will be able to make use of the replacement internal drive?

Internet recovery allowed me to do a fresh Mavericks install on the machine, and I'm currently updating it to El Capitan, from which I'll hopefully be able to get Sierra running, but I'm expecting that High Sierra will give me trouble on the external drive.

Any recommendations?
Thanks!
The firmware updates are now included in macOS installs. Upgrading by installing High Sierra or Mojave to a USB external drive should cause the firmware to be updated. I have a external HDD with a APFS container partition. I installed High Sierra to this container using a 2011 iMac. I also installed Mojave in the same container (to a different volume) using a 2013 iMac. The firmware on both Mac was updated or I would not be able to boot from the external drive. (Although I can not boot Mojave on the 2011 iMac, which was expected.)