Does document expiry update on DocumentAlreadyExistsException

If I execute a document insert but a document with the supplied id already exists, I know that the document content won’t get updated.

However, will metadata (like the expiry value) be updated when this happens?

No it won’t touch the metadata if the operation fails. However, upsert, create and update are all able to modify the TTL if the operation succeeds.
Alternatively, you always have touch and getAndTouch.