With the advent of Watch OS 7 you can share your watch face. I got a new Apple Watch Series 6 and want to keep my Apple Watch Series 5 to use when the battery is drained. Especially now that the watch measures sleep -- though so does my CPAP so I'm not sure if I need that feature. I decided I wanted to set up as a new watch, not a backup, since they have different functions for me. I wasn't sure how to move the Faces from one watch to another but it's quite easy. Go to Watch App, click on All Watches, then make the old watch the active watch. Click Done. Go to the Face Gallery, pick a face, then click share. I saved the face on the phone itself in a new directory. Pick each face and save them in the same place to make it easier. Once you have all your faces saved, go to All Watches and make the new watch the active watch. Next go to the location where the faces are saved, click on each face and you'll get a dialogue to add the face to the watch. Do it for each face and you're good. I didn't see the faces load right away, so I forced them to load to the watch by going to back to the watch app, then selecting each face and setting them as the current face.