The RAVPower Filehub runs embedded Linux, which is a cut-down version of Linux with a low memory footprint. Most of the filesystem is read-only apart from the contents of /etc and /tmp, but changes are not persisted across reboots.
The easiest way to "hack" / modify the configuration of the embedded Linux is to create a script EnterRouterMode.sh on an SD card and put the card in the Filehub. The current firmware (2.000.004) will execute a script with this name with root permissions when the SD card is mounted.
The EnterRouterMode.sh script modifies scripts within /etc and persists changes by running /usr/sbin/etc_tools p.
To use, download the EnterRouterMode.sh script, copy it to the top-level folder of an SD card, and insert it into the filehub device.
https://github.com/dmgeurts/filehub-config
https://github.com/dmgeurts/filehub-config/blob/master/doc/Firmwares.md