I think I would go the Move Tree route. I use it often to rename large groups of files.
I gave that idea a bash earlier but it didn't work as I had hoped.
I signed out all the original files in their folder. Then went to my copied Assembly containing the copied files. I used the move tree command and selected the folder containing the original files as the move tree destination. I then selected the rename option allowing me to replace the appended prefix with a blank (effectively attempting to rename the files with their original names).
It all seemed promising. When I "approved" the move tree command, I even received a message asking if I wanted to overwrite the existing files. I selected "Yes to all" but then received a message saying that I must have unique file names and the file names I was trying to use were already in use. The action then automatically terminated with no action carried out.
So close but so far.