When I was in high school, I was taught basic darkroom techniques for altering film postfacto -- even doing so without doing a negative transfer -- by an old artist friend of mine.

If you're willing to do some basic home chemistry, you can do quite a few things to film during development that will alter in predictable ways the outcome; a favorite of mine is that adding a small amount of buffer solution into your developer and stop bath at the right time can adjust the light curves, which can turn a nighttime photo into a daytime photo if you do it right.