Quarter tone playback Plugin Does Not Apply Tuning (even after updating the qml file to MuseScore 3 format)
The plugin does not apply any tuning change to notes with a quarter tone accidental.
1) Use the python program that converts MuseScore 2 plugins to MuseScore 3 format (see https://musescore.org/en/handbook/developers-handbook/plugins-3x)
2) Install the plugin into MuseScore 3.0.5
3) Create a score, and place whatever notes you want, then place some quarter tone sharp (sharp with only one vertical slash) or quarter tone flat (flat with a diagonal slash)
4) Select those notes and attempt to use the plugin to apply the tuning
The notes with accidentals didn't have their tuning changed.
For example, the file below "quarter_tones.mscz". Several notes have quarter-tone accidentals, but when selected and having the plugin used on them, their tuning remained at +-0 cents. In fact, if you use this plugin on notes already set with quarter-tone tuning (like the notes in the example score in the plugin), it sets the tuning to 0.