Systemd.mount file to take care of the overlay for you. Still need to create upper and workdir. Save as storage-steamlink-udev-rules.d.mount. Put it in /storage/.config/system.d/. Turn on with systemctl enable storage-steamlink-udev-rules.d.mount.
Code
[Unit]
Description=udev rules overlay
DefaultDependencies=no
Before=umount.target
After=systemd-udevd.service
[Mount]
What=overlay
Where=/storage/steamlink/udev/rules.d
Type=overlay
Options=lowerdir=/lib/udev/rules.d,upperdir=/storage/steamlink/udev/rules.d/,workdir=/storage/steamlink/overlay_work
[Install]
WantedBy=local-fs.target
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