I think Charles is effectively doing the job already. The only thing he doesn't do is receive Ambassadors and the PM, as far as I can see.
But the rest of it will be a pretty seamless transition I imagine. I know he doesn't want to live in BP, and I can see that being the biggest upheaval of all at that age.
But the actual dqy to day job? It's wierd that people don't see that it's not gonna be all that different to now.