As a dev I’ve been on both sides to be honest. Especially when there is pressure to finish the next task. I think it needs good planning to create enough time for these things.
In the end bad devs will still shut you up about things they are not interested in fixing…
I think https://github.com/KMKfw/kmk_firmware might be what you are looking for: It exposes itself as flash drive in bootloader-mode and the files on there are just regular Python scripts. If you search for “KMK macro pad”, you’ll find a bunch of projects - most of them diy. If you want to start from scratch, Jan Lunge created an awesome tool for setup and keymap adjustments (video https://www.youtube.com/watch?v=RtYJYFMWjNM, repo https://github.com/JanLunge/pog) - with the idea being that after setup you do not need the tool anymore to adjust the keymap.