[I am not so sure how to switch to via de la plata.../quote]
Sorry I was not very explicit. The Camino de Invierno joins the Via de la Plata near Lalin, then the 2 run together. There are caminos that lead north off the Frances but I don't know where, one goes from Leon I think.
Probably the only way of getting to the Via de la Plata, from the Frances, would be to leave at Astorga and follow the signs backwards to join near Puerto de Sanabria. I've no idea how you would do that, it would need careful planning I think.
If you really don't want to walk from Sarria it may be possible to get the bus to Lugo and then walk from there. Again it is not a route that I have done. I think it maybe the Camino del Norte :?: or the Primitivo :?: Someone may come up with some info.
If not just try and enjoy the crowds
Sue