Hi Fr. Tom, I’ve walked “backwards” several times, on the CF and the CP. It IS doable, although you will get to many intersections where you are unsure which path to take. If a pilgrim is coming towards you, then no problem. If not, it may take a while to get onto the right path. Be prepared to frequently get lost – or not where you are supposed to be. Once you cross into Portugal the way is waymarked with blue arrows to Fatima.
Not only pilgrims, but many locals will tell you that you are going the wrong way, so learn how to say that you are walking to Fatima, or Rome, or wherever, so that they can stop worrying about you.
After a while I did get kind of lonely. Every night there are different people, who are already in their little camino groups, so it can be a bit difficult to meet others to spend the evenings with.
It IS a challenge, in more ways than one, but, yes, doabl