In the older days it was not that straight forward if you wanted to copy, rename or delete overlays and file sets, but that is actually possible via the InterForm400 menu in a fast, simple way. This has been possible for quite a while, but this feature came as a surprise to some so perhaps you also could use this information. To do that you select this in InterForm400:

80. Administering InterForm 400

2. Work with file sets

Now you can copy, delete or rename file sets and if you select option 12=Overlays in file set you can even do the same with the overlays. Just notice: Renaming an overlay will not update any references to this overlay. So you will need to do that afterwards if needed.