depending on the brand of die, you can chuck it in a lathe and shave the base with a carbide insert or better (I prefer ceramic inserts). It's a good idea to use a spray mist directly ontop the insert to keep the heat out of it. Your probably not going to draw the heat treat back enough to matter with the heat involved anyway, but you absolutely want the heat to be in the chips and not the part. If the chips come off super hot, your about right. You can get this by changing the spindle speed. After you remove the metal to change the length of the die, you will need to cut a very small chamfer and then radius it with some emery cloth followed by the same thing in 400 grit black paper with a little oil on it (I recommend using a small wooden dowl. Thirty thousandths is about right for the radius. Spindle speed will vary with the metal alloy and heat treat, but a good place to start is around 400 rpm with a ceramic insert and then adjust from there. I used to slice A2 drill bushings at 600 rpm all the time with little heat retained in the part.
gary