Using a mill would be the best way to mod pretty much anything I would think... but, if you've got a steady hand and have a good idea of what you're getting into, and what to do, then doing the mods by hand will be just as effective IMO.. the small imperfections will make a difference but probably not enough to notice if the overall job is done right.
And.. I didn't polish the crank to a mirror finish like most that you see (including the last crank I did), I'm just trying something different this time around, I guess
....some of the parts I modded are polished to a mirror finish (on the intake side) but not all..