Originally Posted by rybolt
Just as a tip for anyone else going through this problem, a user over at the Fuji X Forum suggested a program called A Better File Rename. It lets you customize and change the name of a batch of files without affecting exif data or anything else. I downloaded ($20) and it worked flawlessly.
For Mac, I use BatchFileRename. It was something likewise-in-price
and has worked flawlessly for several years on my Mac Mini now.
In Nikon DSLRs you can set up a prefix for the filename, which I have always found very useful. I did regret to find it absent in my Ricoh GXR when I received that.
Another method is to import the files into Lightroom using an import rule that will add a prefix, and use different prefixes for both cameras. But, you gotta be a Lightroom user to do so... and it still doesn't remedy the file-overwriting issues you get into when you switch cards in two cameras while both cards still have some files on them and the filenames are identical!