Hi! I had the same question but found no answer, until I tried by myself
Download kingroot apk from your tablet, install it and you get root.
Next follow the guide posted in this forum.
But here's the trick: you can't go back after you flash the old bootloader,
So reboot to recovery and push the zip to sdcard
And boom new ROM installed.
Don't worry if you reboot to stock, you get black screen but not a brick, get back yo fastboot, reflash and reboot to recovery