Adding a cinch cord to the hood of a down jacket?

If the edge of the hood is finished with piping (like a lycra edge) you can just open a small section of the stitching at the bottom of one side of the hood opening and use a very small safety pin that you poke through the end of a bit of fine elastic cord and inch-worm the safety pin through the lycra piping all the way around the hood opening. Open a little of the piping seam at the other side of the hood and pull the safety pin/elastic cord out, add some cord-locks, and voila, you are done threading the elastic all the way around. It is a little tedious and can take a number of minutes to advance the safety pin the whole way, but it works in many cases. I did this recently to my wife's puffy.

Thanks Philip, that's a good idea. I want to do this as well, but was hesitant about sewing another channel over the piping because I didn't want to loose the inherent elasticity. I'll give this a try!

Another option is to sew another layer of piping or bias tape around the edge. That way if you mess up or don't like it, you can remove it.