No, there's no way to dull the sharp edges of the mag-tube slot without also removing some finish.
Find a piece of round wood dowel, a round marker pen or something similar; wrap it in emery-cloth or sand-paper, slide it back and forth in the mag-tube slot until the sharp edges have been smoothed out.
You can touch-up the bare metal with a cold-blueing product, but chances are that you'll wear it off in a short while since your left hand will be gripping and rubbing against this area....