I know a guy who is re-triming his Recaro (fabric) seats with brown leather, and he's doing it all himself.
I don't know how far down the road he is at the moment, but the last time I saw it he had almost finished one seat. It looks very difficult and hugely time consuming but you must get a huge amount of satisfaction from it.
He did say, however, that he has had a lot of prior sewing experience. Which I would say is essential!
Toby