WP: I appreciate your intentions, but unless rules have changed this year, they don't allow adding alternate leaders to a permit after the permit is reserved. They do that to prevent scalpers from selling permits to the highest bidder. ...and unless things are different, you don't get a refund on your permit when you cancel. If things are not as I think they are, please write and let us know what works.
In the past, all you could do, (and I would urge you to do it) is log onto Recreation.gov and cancel the permit. Then the slots will show up (randomly in the next 24 hours) so someone else can reserve them.