I do small MODs too. I do a little of everything really. Also did some GM MIDI when I was hooked on J2ME development. (Old cellphones before Android and iPhone came along).
Here's a recent MOD of mine in only 79,496 bytes, using filters and stereo.
https://indiegamemusic.com/4556
And an older one in only 34,190 bytes.
https://indiegamemusic.com/84