Do you have access to a small belt sander, the portable ones with the 4" wide belts?
If you do, mount it so the belt runs vertical, but towards the ground. Grind and dip into water often. Use a 100 grit belt and go slowly. You will transform it before your eyes. If the blade is too hot to hold with your bare fingers, you have made it too hot - dip often.
If you cool it with water often, you will not damage the hardness.
Alternatively, you could use a Dremel type tool with lots of cut-off discs. Eventually you will get it to the shape you want. Just had a thought, using a dremel with a cut-off wheel, score the shape you want and you may be able to bend/break off the bits you don't want. Then touch it up with the dremel.
Please be sure to wear safety glasses.
Oh - did I mention to dip it often....grin.
Cheers,
D