I would be very, very careful about dehorning a Lightweight Commander. The frame is anodized aluminum, and if you cut into the anodizing, you will need to have it re-anodized or coated. If you cut too far, you will be crying the blues.
Take a grease pencil and mark off the areas you intend to cut down. Then set it down for a few days, and go back and study it. Once you are sure, really sure, start work.
Use a fine file, and have a file card close by to keep it clean and cutting well. Get a pack of wet/dry silicon carbide paper and a can of light machine oil to wet it with.
When you do the work, only take off about 2/3 as much as you have marked with the file. When you use the cutting paper to smooth and blend the cut areas, you will take off the rest.