Forget the Dyson site - the usual disclaimer about competent electricians, hence cannot give advice etc.
Advice below is how I did it - but be careful as the bits are held on by flimsy clips that break all too easily (sums up my DC03 experience - will not be buying another).
As in my case the cable sheath had split just at the cable entry point, I just shortened the flex and refitted. It was too damned short to start with, so little loss in convenience, as still have to use an extension lead.
Menit Mesenn, April 2006