I was watching some of the coaches press conferences, I don't remember who it was, maybe Dom Capers and Joe Whitt, anyway they basically said Charles Woodson would play all over the field. Corner, Nickle, Safety, Linebacker. One of the coaches said that Woodson played the Philadelphia playoff game a couple years ago as a Mike linebacker.
It doesn't really make sense for anyone to say "Woodson will or will not play this or that position" he's going to play all over the field, that is his biggest strength, he's a damn good football player no matter where you line him up and they will play him all over the field depending on the situation/opponent.
I don't know if he would ever switch to Safety full time, as that really limits what he does, which is a hybrid corner/safety/linebacker jack of all trades type player.