If you reboot, you loose your change...
Not when you save the changes to /www/pages/cgi-bin/minerAdvanced.cgi on the Z9 mini.
I believe what Django69 meant was that the changes are lost when the z9 mini is powered off, not reboot. The OS is running on non-persistent storage and any changes to the file system are lost when powered off. The config (ie. /config) on the other hand is kept on persistent storage and any changes here are retained.
When powered off, you lose your customized web page but your OC setting will still be set to what it was before the miner lost its power.
Good discussion guys. Thank you!