AeroPod, PowerPod and Newton

My iSport is working pretty well with my first Est CdA and Est Crr setup and a Calibration Ride. But if I now enter new values in the Est CdA and Est Crr screens, or if I go ahead and do a Coast-Down Calibration, should I then redo the Calibration Ride or is this not necessary?

No, you do not need to red-do the Cal Ride. The Cal Ride determines wind scaling and riding tilt factors, which are not affected by changes to CdA and Crr numbers.