Try doing what I did. A lot of coaches are the same coaches just with different names. With Ray Horton I just changed the Cardinals defensive coordinator's name to "Ray Horton." (Double clicked on the name and on the left side it has all his attributes) For Andy Reid...just use Andy Reid. There is an option where you can re-assign that coaches team. Just change it from the "Eagles" to "Cardinals" or whatever and for Whisenhunt change his from "Cardinals" to "Free Agent".
If you want Ray Horton to be the Head Coach: rename the Cardinals defensive coordinator to "Ray Horton" and change his status from "Defensive Coordinator" to "Head Coach." But, also make sure you change Ken Whisenhunt's Team from "Cardinals" to "Free Agent."
Essentially you're treating the Head Coaches like player transactions. Moving them from one team to the next and from one position to the next. Instead of just renaming coaches. That would be like me changing "Tom Brady" to "Peyton Manning" and getting frustrated because he looks like "Tom Brady." All you did was change the name.