Python MIDI Modifier Script

I have a single-purpose task in mind: I need a Python program that takes any standard MIDI file, shifts every note up or down by a user-defined number of semitones and, if requested, swaps one General MIDI instrument patch for another across the whole file... (Budget: $10 - $30 USD, Jobs: Audio Processing, C Programming, C++ Programming, MIDI, Python, Scripting, Software Architecture, Software Development)