I think the change of details has to be done pretty soon, scoobydoo. I don't have my info with me, but it could be the end of this week.
You'll be fine for the cycle - the first 10 miles are downhill, then it's flat for a good while, and there's only one significant hill that a lot of people push their bikes up (I've never had to do that yet, even last year when I'd only been out on my bike twice before the race......)
Go on, you know you want to.......