Though there's no built-in functionality in MuseScore to do this, you can write a plugin that controls the mix for each voice. See this forum topic, which is qu

Though there's no built-in functionality in MuseScore to do this, you can write a plugin that controls the mix for each voice. See this forum topic, which is quite similar to what you're trying to do: https://musescore.org/en/node/56916 https://musescore.org/en/node/56916