When writing or importing music, a composer sometimes writes with no key signature, but may have many accidentals that are written on a per measure basis. The way it is now, the score editor seems to randomly decide whether a note should be written as a sharp or a flat. Example: A# or Bb. If you use the Key signature feature of ProTools, it removes all the accidentals.
One way to do this would be to use the key signature option, but have the option to "Leave accidentals in score and not have the sharps and flats at head of measure".
Another way to do this would be to have an open key signature, and one would highlight note groups or select measures and then choose: "Write selected accidentals as sharp" or "Write selected accidentals as flat".