I’ll check after work and see where I read about the MuseOn modding, I could be mistaken.
Are the buttons in the MuseOn completely self-contained? Or is the black bezel around the buttons part of the MuseOn? If that’s the case, you could mod it similar to installing Sanwa buttons in a KOC. Basically grind the faceplate’s bezels flat, widen the KOC button holes to accept a Sanwa key, remove the box area that’s inside under the original keys, knock out a hole in the bottom of the key panel and controller, and attach the controller to some wood or something (since the keys’ bottoms will be sticking out). Wiring can go a few different ways, but for lights, if you use a separate power supply (you need to on a KOC since there’s not enough current from the PS2 to power all 7 Sanwa key 12V LEDs at once + the controller, even if using one USB port for separate power) you can use a small circuit with two diodes to block the LED power supply from interfering with the KOC’s PCB, and to make the buttons light up of course.
If putting new buttons in a MuseOn is similar to doing it on a KOC, it will definitely be a weekend project. I’ve almost finished my Sanwa modded KOC, it took a lot of work to get it where it is now, you can see it here near my horrible ugly ghetto ASC lol, which definitely didn’t take very much work: