I can manage this with a fairly simple bit of scripting. Something like the one below. As Frankco pointed out, Outlook does not allow an attachment to be renamed. To enforce this the FileName property of an attachment is read-only. What this code does is automate the process of saving the attachment to disk, renaming it, and reattaching it. The code works against the open message. It doesn't care if the message has been sent or not. The lone restriction is that it only handles one attachment, the one that's first in line if there's more than one attachment. We can change that though if needed.
