I see no real reason why you shouldn't do some sort of reverse heel shape, though it's debatable how stable the blade would be. I strongly advise you not to use a chainsaw file however. Firstly, it shouldn't be hard enough unless you propose annealing the razor, and secondly the aggressive cutting action is as likely to shatter the blade as anything else. Far better would be a smallish carborundum wheel in a Dremel or similar, dipping the blade very frequently to keep it cool. Be careful, there's scope for mishaps here.