This is easily possible. You can simply change the relevant fields in the Receive at... field in Settings/Messages (and FaceTime). You need to add the alternative email address before you delete the original, because there must be one there at all times. This doesn't change the AppleID associated with the device. My iPad and iPhone and my son's iPod and iPad are set up this way, and we do not receive each others messages or FaceTime calls.
EDIT: All four devices use my AppleID.