I tried this method, however the aml_autoscript.zip never appeared in the update&backup list. Didn't seem to pickup the SD card. So I tried the toothpick method. The box booted to the Google splash screen, sat there and eventually the screen went blank. I then tried booting to Recovery, but I could not install the script from there. Tried twice, no go. Then I booted without the toothpick and as soon as the Google splash came up I inserted the toothpick. The Libreelec boot came up and installed 18.2. So I am up and running on an MXIII-G 4K.
Have to say, this box is still fast and runs great. Definitely worth the effort.
Thanks again Demetris.
Update - I can't play anything, as selecting any of the options - pause, stop, play, fast forward or reverse locks up the device. So I'm back on 8.2.2, which is working pretty well.