That is something that never occurred to us. Certainly would be great if you could just drag & drop it, but it’s not going to be that easy. Do you expect that this would be a common use case?
You should probably just delete the transfer from NPC and repost it from the correct project.
You could open the record copy ZIP file before deleting the transfer. You can then extract the files somewhere on your local disk and recreate the transfer by selecting the files/folders you extracted. After creating the new transfer, you can delete the old one.
It might help to have the transfer form open so you can copy/paste the subject etc. into the new transfer. You can do this with 2 running instances of NPC to make the process easier.
Unfortunately, this process loses any history associated with the file transfer such as downloads. You can copy and paste the history from the transfer form and put it in the remarks of the new transfer just so it is not lost entirely.
Of course, anything can be accomplished if we edit the XML and copy a few files but I’m guessing that is not something we would want to do unless we absolutely had to.
Not a great solution, but hopefully there are a couple of tips in here that make it less painful.