These are not complete files.
These are XML chunks that you need to incorporate into the respective XML files under /Applications/Dorico 3.5/Contents
(right-click the app and choose "show package contents").
They provide Sketch Treble, Sketch Alto, and Sketch Bass instruments. Each instrument is a single staff played with a piano sound, and can be condensed.
Additionally, edit instrumentFamiliesDefinitions.xml
and add instrument.keyboard.piano.alias.sketchtreble, instrument.keyboard.piano.alias.sketchalto, instrument.keyboard.piano.alias.sketchbass
to the `` list for instrument family.keyboards