Just realized something! The instrument patch I shared only works for the game, Fire Emblem 7.
Instrument patch is a UPS patch that only works for FE7. Here's a raw hex version of it that you can paste into your ROMs manually.
And paste it in your ROM at the offset 0x11C3AC0 (expand your ROM if you don't have that offset). That expands a ROM to about 20MB, so if you're warry about that sorta thing, you can also repoint the table to your own offset.
tl;dr summary for my version:
Patch your ROM/Paste the dmp at offset 0x11C3AC0.
When inserting MIDIs, reference the instrument map at 0x12F471C.