Ahh - I have found the answer..

Instead of unloading the module, modifying it and loading it back in - all I had to do for the Omega (sorry called it an onion earlier) was to add the following to /etc/modules.d/usb-serial

usbserial vendor=0x05c6 product=0x9000 maxSize=2048

This permanently adds the product and vendor ID's and they now get loaded on boot. I bet that this is a solution for many USB to serial devices. Learn something new every day.!

Now when I look in /dev I see the following:

root@Omega-1F15:/dev# ls tty* tty ttyATH0 ttyS0 ttyUSB0 ttyUSB1 ttyUSB2 ttyUSB3 ttyUSB4 root@Omega-1F15:/dev#