My experiences with crontab @reboot is that I dropped that solution in favor of systemd services.
To give you basic idea here comes a excerpt of code I put into the customize-image.sh script:
cat <<EOT >|/usr/local/bin/usb3-memory-size.sh
echo 1000 > /sys/module/usbcore/parameters/usbfs_memory_mb
chmod +x /usr/local/bin/usb3-memory-size.sh
cat <<EOT >|/lib/systemd/system/usb3-memory-size.service
Description=USB3 memory sizer
ExecStart=/bin/bash -c "/usr/local/bin/usb3-memory-size.sh"
systemctl enable usb3-memory-size.service
It creates a new service that corrects the kernel setting for USB3 camera.
This works perfectly fine.
When such a service shall be triggered depends on your configuration. Look at the line of [Unit] section, explicitly before/after lines.
For example you can force such a service to start after login prompt pops up.
Sorry to jump in on this only now (because I only started some weeks ago in trying to bring some gpio-spi stuff to work.
This general SBC library approach looks very interesting to me, and I wonder how experienced GPIO/HW/SW technicians see it? Would it deserve more attention? Or had it some drawbacks because it can't be so low level and direct as device tree, libmraa ecc... ?
I saw the request to post issues on the github repo, but I believe this is not an issue but more a request for better understanding.