I know that for the Avid SL rim brakes, the difference between front and rear is in the brake pads alone. The replaceable pads are locked in different directions, so that they're always pushed into their slots when you brake. The rear brake's pads are pushed in the opposite direction of the front ones. If you, like me, use different brake pads from the start, then they're identical.
I don't know, but I assume, this is true for most or all rim brake types.