Yes, as poker says, it's quite easy. Just look where all the leads go on the connected one before you change it over and plug it in the same... you can plug it in in serial to your main hard drive and have it as a secondary one. I have a removable tray on mine, so I can take the HD in and out whenever I please... that way I can back up and either take it with me if I'm travelling, or in the case of the fires recently, I just stuck it in my suitcase and knew I hadn't lost everything
THIS is what I'm talking about. You could get extra drawers and swap two or three HD's in the same tray.