Probably hard, often the head snaps off as you say. Consider what your next step would be if this happens.
I'd try a combination of the funkness attached to the harness loop (may need to be extended) with the peg at waist level. Push with your legs to apply a sustained outward force on the peg. Simultaneously, tap the head of the peg side to side if in a horizontal crack, up and down in a vertical one. If some of the blade of the peg is accessible, you could try tapping the blade directly by using a chisel or centre punch which might lessen the chance of snapping the head off.