How to update OpenWRT while retaining existing configuration and all custom packages
OpenWRT upgrades itself by saving configuration files from known locations (plus manually defined files), overwriting the partition with the latest firmware and then restoring the saved configuration.
This usually works for the configuration itself, however the process doesn’t take care of any custom packages that were previously installed manually (either through LuCI or with opkg). These packages need to be noted down beforehand and then reinstalled.