You can also expose the film to fumes of hydrochloric acid, or mix a little sulfuric acid + potassium permanganate + sodium chloride in a 'gassing tank' (tank reserved for the process), load it in, a spacer reel at bottom so film doesn't get wet, that's a dry process and works well too.

The other idea to do, is sleeve some film in plastic and leave it out in the sun for a week, to 'print-out', the grain will be much much finer. Gas bleach it back, ultra slow very fine grain film.