Lynn, I am 39 and have been racing bikes with CMT since 1990. I am a 2 time Paralmpian and medalist and now working full time as a cycling coach. I cannot stand up on my pedals anymore under anything other than relaxed conditions. I just stay seated and stand for a bit whenever I can to stretch and move around. This means that in a 30 minute - 2.5 hour race I ma not stand at all, but it is what it is.
My biggest concern for you is doing a 200 mile event. That is extremely hard on a body and everything I've see, experienced firsthand, or heard from anyone indicates that this is something that should not be taken lightly. I would never recommend that a coaching client with CMT do this ride.
A few of us have found high intensity and high volume training and racing to exacerbate the deterioration of CMT. You get tired and never get back from it. Doing a century is one thing, doing a double is more than double the stress.
If you just have to do this ride, I'd strongly recommend training allot more than 100 miles/ week. An event like this is possible, but be prepared for some very un happy effects. You may not have any problems, but you may experience some significant loss of strength and fatigue that you may never really recover from. Go into it knowing what may happen.
I have been struggling with retirement from racing for several ears now and I'm fairly sure this will be my last. My body just won't do it any more. My legs are loosing strength and I am exhausted from a 3 hour training ride. Sometimes an intense 45 minute ride is too much, and sometimes a 3 hour easy ride will take 6 days to recover from.
I hate being the voice of doom, but 200 miles in a day is hard for anyone let alone someone with CMT. LIke I said, if you want to do it, go for it! Just make sure you are ready.
There is no reason for you to quit riding, in fact I think something like cycling is necessary, just be smart.
Anthony Zahn