ChangeSubject changes the subject of the message of the document or the message for the given Guid. The change is logged in the status history.
ChangeSubject (FileName, ['Attachment GUID'])
ChangeSubject (concat("Message from ", ActualDateTime("yyMMddHHss")))
ChangeSubject (concat("Message from ", ActualDateTime("yyMMddHHss")), GetDocument(GetDocument()/@OriginDocumentId)/@MessageId)