In the interest of time, could you please write an MR for this @leo-singer? We're planning for the next gwcelery release to include SSM, so having this functionality in gracedb-sdk would be very helpful. I believe you could write an MR in very little time, which should be weighed against the much longer amount of time that a non-gracedb-sdk maintainer would take.
Alternatively, I still have an MR somewhere to go back to the stock gracedb API, which has all of the functionality that we want.
wherever gracedb_sdk makes the POST to write a log message, there just needs to be an optional keyword argument label: [str] like here, which will apply the label to the parent object (event/superevent) after writing the log.