Presumably you've googled "Hex Editor Windows", tried the many hex editors that you'll find there, and found none of them satisfactory?
If have thought of doing this, could you give us a list of the ones that you've tried, and why they don't suit your purposes.
If you haven't already done so then I suggest that should be your first course of action. (BTW, if that is the case then I hope it's just a question of editing files rather than direct editing disk sectors!).