No... you can't do that. Even if they renounced Childress they wouldn't have any room to sign Arenas. Not even close. When your owners want to you can go over the cap to resign your own guys, not guys off of other teams.
Again...the Hawks have very little caproom even WITHOUT Smith and Chil. You can renounce whoever you want and it won't matter. It's impossible for us to get Arenas unless he's willing to take a massive paycut(which he isn't) to come here.