Well so far so good ds is coping well. We're indulging his interests,we're enjoying watching him recall minute pieces of information from nine years ago and I've given up the front seat so as he can navigate from his memories of nine years ago faultlessly. Dh and I have also given up the master bedroom as the room that should have been his wasn't "right" can't work out whether it was the duvet cover, the window being too close to the bed or whether it was because the room was too near the back door so we are now on a sofa bed and ds is in the king size four poster 
But it seems to be working, ds is in the most part quite pleasant (for him anyway) and is happy sat in a deckchair on the beach watching the sea (he's very cheap to entertain) Dd is pretty hyped up but bearable so long as we get out of the rented cottage for a good part of the day anyway. Fingers crossed this continues.