I have the current work-in-progress version of MIDI-MIS (MIDI file Musical Instrument Switcher) available on my Google drive.

https://drive.google.com/drive/folders/114K2TuMGXu7w_vX-iBWI0Kf9RCb9wi6K?usp=drive_link

MIDI-MIS is a Windows application created with Game Maker Studio allowing easy viewing and editing of instrumentation in a MIDI file. It is capable of modifying GM, GS, and XG files (though the current concentration has been on GS). It came about because I needed to be able to edit MIDI files I am creating for the SNES MIDI Remaster Project.

Features:
- Change any instrument in a MIDI file to another instrument, using one of three methods:
change instrument on a single channel
change instrument across all channels, as originally assigned
change instrument across all channels, as currently assigned (modified)

- Modify the pitch of any instrument in 1 semi-tone increments, with same methods as above

- Convert between the three major MIDI file types, GM, GS, XG using SYSEX (*currently only GS conversion implemented, results may vary)

- Ability to load custom instrument lists to match your specific software/hardware (*currently only custom GS implemented)
Default comprehensive lists included for all GM, GS, XG

Additional info included in the project documentation.

* As this is work-in-progress software, please always back up your files before editing. Bank Select MSB and LSB values are added in to all files for editing purposes.

GM (*display, actual file is GS):

GS:

XG (*display, actual file is GS):

Standard VS custom instrument names:

Pitch shift demo +24 semi-tones: