OK So I can just drop tar I proposed into update folder on current running LibreELEC-AMLGX.arm-9.1-devel-20190512121532-df6beb1 install and switch to box image/build, with minimum effort and assume I will I be able to boot between android running on emmc and libreELEC on SD which was case until recently. (Not sure which recent LibreELEC build, boot between SD & EMMC stopped working for me)
Thanks for explanation about "box" image, will update later this week. (Will make sure to take LibreELEC backup before attempt latest update)