I haven't started using Custom Tags yet (this discussion actually brought this subject back to my mod/content team).
But, I do know a bit about how they work, and yes, structurally they were/are kindof the precursor to Care (I think that's how my Acct Team put it).
Anyway, enabling custom tags opens up another backend location called "Moderation" at the top right beyond Admin / Studio / Publishing.
In there you'd have a list of things custom-tagged as "Externalize" but it's unclear to me how you might take the next steps in the workflow.
Maybe someone else with on-the-ground experience will have better advice.
Worth a look anyway.
