FYI: Did the Philadelphia Eagles pull a fast one on the Dallas Cowboys?

This question was asked on another forum by HRF12:

During Monday night's game with the Eagles, Donavan McNabb played the quarterback position most of the game. Backup quarterback Koy Detmer held for field goals and extra points. Mike McMahon came into the game in the 4th quarter to play quarterback for the last series of the game. How can this be? Please correct me if I am wrong, but the only way the third string quarterback can enter the game is if the first two are injured. Detmer was shown on camera preparing to come into the game. What is the deal? Did the Eagles pull a fast one?

Feedback from LeonDixson from a sports forum:

This was answered in a column the other day. It might have been Mick's mail. I don't remember. Anyway the answer is that the rules were changed a couple of years ago to allow you to play the 3rd QB in the 4th quarter without forfeiting the right to bring your other QBs back in. It was changed to allow teams to give developmental players some playing time in blow-out games. I've never seen a team do that though.