I have two drones. One has a camera, and I might use it commercially at some point. It could carry a Remote ID transmitter. The other does not have a camera, and has no use other than recreational flight. It's way too small to carry any "cargo." If I get a remote pilot certificate to be able to fly under Part 107, can I still fly the unregistered drone under the exemption for recreational flyers after Remote ID rules take effect?
Yes. If you hold an FAA Part 107 license, and you are not flying in a manner that requires a 107 license, you are free to fly as a recreational pilot. See here: https://www.faa.gov/uas/recreational_flyers