| It might alter the tone somewhat. I've found that neck mass can effect tone-at least, it did when I swapped out a P neck for a Jazz. I can't say for sure it was just a difference in mass though. I'd be careful to not take too much off the neck because of loss of stifness. It's hard to tell how much is safe.
You can finish the back of the neck, once all the old finish is removed, with something like Minwax antique oil finish-a blend of oils, polyurethand and thinner. Multiple coats will protect the neck from moisture and you can steel wool it to a satin feel that won't drag on your thumb when you play.
I don't know what tools you plan to shave the neck with. You'll have to make sure that you know how to use them skillfully. | 
