I created this program after fiddling around with MIDI files (for another project) and being dissatisfied that there wasn't an easy bit of software that you could use to change the instrument of a MIDI file without importing it into a complicated DAW. I then learnt how to edit the instruments manually using a hex editor, then I decided to make a much easier to use program.
It's a simple python command line utility, as I didn't want to spend too much time writing it, but it definitely does its intended job well!