I worked with ARJ archives well into 2015. At one point I studied the format to see if it was possible to change the filenames in the archive without unpacking/

I worked with ARJ archives well into 2015. At one point I studied the format to see if it was possible to change the filenames in the archive without unpacking/repacking. It was. And I did. To be fair, I had ~230k files I had to "manipulate", so even automating a unpack/repack would have cost too much time and energy.