OpenWrt luci-app-attendedsysupgrade
The OpenWrt luci-app-attendedsysupgrade package allows you to upgrade your OpenWrt device, retaining BOTH settings and the installed set of packages.
The luci-app-attendedsysupgrade package creates a list of all custom-installed packages, requests a build of the new firmware containing all those packages, and then downloads and installs the firmware.
Just under five minutes to get updated to the newest firmware.