Changing labels on a post without using edit api

We are working on creating a fast and easy way for our moderators to label topics without them needing to go in and edit the post each time.  We've been able to get it working using the Message edit API but unfortunately when this is used, the "read by moderator" flag is placed back on the post and the moderator is forced to refresh the page anyway to get the moderator flag removed which kind of defeats the purpose.

So I was looking to see if there's a way to edit labels without needing to use the message edit api.

I noticed there is the labels api: https://lithosphere.lithium.com/t5/Developer-Documentation/bd-p/dev-doc-portal?section=commv1&leaf-id=Message.labels#Message.labels.labels

If lists supporting both GET and POST methods but there's no documentation under POST.  Anybody know if it's possible to use the POST method to change labels on a message directly?