Both need to have the PGM / RUN switch in PGM when changing the IDs. You can do one at a time or since they are getting the same ID you can do them together. Since these are newer AA sets they are factory programmed to operate together using the same ID. The rear facing unit will run in reverse. If you want to prove this leave them uncoupled and assign them the same ID. Start them out and the second unit should run in reverse.
Yep, all the recent ones I've seen have been configured this way, makes it easy to configure them.