I'm not 100% sure I understand what you mean. Do you mean start another Camino immediately after arriving in Santiago?
If so, you could walk back along the
Camino Frances. It's probably the easiest to walk backwards as it's so well marked, and you also have a stream of pilgrims coming towards you to reassure you that you're on the route. Or you could do the Camino Ingles, Camino Portugues etc in the right direction after getting a bus/train to a suitable starting point.
One of the issues with walking backwards is that in all likelihood you'll be the only one. You'll meet people but they'll be 50kms away the next evening so you won't form the same friendships.
Buen Camino!