Set output to stack in groups of 500

I assume that what you mean by "offset every 500 copies" is that you want to invoke a feature which can physically offset the stacking of copies in the printer's output bin. Assuming that is what you are trying to do, there is nothing that you can readily do in PostScript itself to achieve this.

All device controls are performed via the setpagedevice operator which is quite specific to particular printer models. Output tray selection and options such as output offsetting are controlled either via the setpagedevice operator or via the printer's control panel. In terms of output offsetting either by the copy or by the job. FWIW, I have never seen a printer that has such controls for every n copies of a particular job.

One workaround, albeit a bit clumsy, would be to set the printer to offset for each job (not copy) and then submit the same job requesting 500 copies twenty times! Yes, I know that is not optimal, but it would/could achieve what you want.

Beyond that, I would recommend consulting with the Technical or Customer Support organization of your printer vendor.

          - Dov