ProRen requires Kickstart/Workbench Version 39+ and MUI3.8 at least.

Further you need about 50 Byte per file. This means, that you need about 50 MB, if you rename 1.000.000 files at once. As such an anim would be more than 11 hours long, I don't think this should be a problem. Anyway, somebody who does that long animations, surely has the memory. To cut memoryusage down, you could rename the files in more than one pass.