Actually there is a distinction between SIC (COP entry) and PIC ratings in JAA, however some countries, especially the UK, choose not to use that distinction (remember, licensing is still national law that incorporates some european requirements, not direct EU law like EU-OPS). In countries which support that there are some restrictions. With a COP rating you can obviously not fly as PIC and are restricted to flying on the usual copilot station, in transport aircraft the right hand seat, with a PIC rating you can only fly the usual PIC station, the left hand seat. If you want to fly in the other one you need to get special training and checking every 6 months to show proficiency there.