I tried doing this, but firstly, there was no firmware folder within the customizer folder. Even if I created one, the resulting files on the SD card did not include the firmware.
I have managed to get it to work though by doing the following.
I created my SD Card folder and dragged the contents to my card, I then copied uk_new_opt.img over to the root of the Card and renamed it to new_opt.img.
Put the card in the reader and rebooted and I was able to do option 4 then 6 and it worked.
Thanks for your help.