The police cars are "stock".
By stock I mean, they get sump protectors, gearbox protectors, they actually get SOFTER suspension (It's noted as being FE1.5) FE2 is in the S and SS range, being 20% stiffer then normal commodores.
FE1.5 is 15% stiffer, this is done to allow the cars to hop the centre islands in a more controlled fashion.
They get better brake PADS in them.
The older Police cars (And I'm yet to confirm if they still do it in the new ones) also ran a mildly different tune. And by tune, I mean they raised the idle so the police comms equipment didn't drain the battery while sitting idle for long periods of time (IE, Radar duty).
They're definitely not lower, as they have to be able to jump gutters quickly, lowering them would end in devastation...