If this is just to update any usernames that might have been changed, rather than using an ID and looking up 1 user at a time, can you not just use the first method you mentioned with usernames? If you request users a,b,c,d etc… and only get back a,b and d, you know c must have changed and then can do a single lookup using the stored ID you have for that old username to retrieve their new username. It’s not perfect, but it’s less calls that doing it 1 user at a time.