Emulator button config?

Any way to do it on mupen and vba?

I don’t see why not, if you can’t figure it out directly within the emulator you can always use a keyboard & mouse emulator like JoyToKey to set your buttons. I’ll leave some links below. I’ve recently been playing some NES & SNES stuff on emulators, and have been using a bunch of IPS Patch mods/hacks with them, they’re very easy to apply with Lunar IPS, and good ones can really change the game completely for a whole new playing experience.

Mupen controller setup: https://code.google.com/p/mupen64plus/wiki/ControllerSetup

VBA controller setup video: https://www.youtube.com/watch?v=_UV7Fyb7YBM

JoyToKey Download: http://joytokey.net/download/JoyToKey_en.zip

Lunar IPS: http://fusoya.eludevisibility.org/lips/