Hi Teresa,
Did you try the above option?
You can enable Adapter Specific Message Attributes(FileName and DirectoryName) in both sender and receiver channel.
Follow the blog and just use variable substitution to set the DirectoryName in attribute interface_name
I believe FileName will be maintained same if you enable ASMA/FileName in both sender and receiver channel(you can mention dummy name in receiver channel).
As mentioned by the author in CAUTION, it will not be the best way, but still you can give a try and see if you face any other issues by modifying the message header interface_name
Regards,
Zameer