My new bars were hard to get back in as well. Mine were powder coated and I didn't sand enough of it off the hexes before I put them in. They were greased well.
So obviously sanding off the coating is necessary but is there any worry about damaging the (heat-treated?) surface of the hex area? Evidently, nicking the surface of the spring elsewhere can lead to a failure due to how torsion bars bear the stress.