As an alternative to Stream Deck, you can take a look at a Lua scripting approach that I recently introduced. Especially since you already got accustomed to the tricky bit (keycommand editing via JSON), it might be worth your while. You could set up two ‘tools’ for the playing techniques by adding this (which I just copied from a quickly recorded macro; it’s probably possible in a less verbose way):
addTool("add up bow", [[UI.InvokePaletteButton?PaletteIndicatorID=kPlayingTechniquePanel.pta.stringsUpBow&PaletteSectionID=kPlayingTechniquesStringsPanel&PropertyButton=false&SetOldValue=false&Set=true&UseLocalOverride=0]])
addTool("add down bow",[[UI.InvokePaletteButton?PaletteIndicatorID=kPlayingTechniquePanel.pta.stringsDownBow&PaletteSectionID=kPlayingTechniquesStringsPanel&PropertyButton=false&SetOldValue=false&Set=true&UseLocalOverride=0]])
… to the framework’s tool setup file.
Incidentally, I hope to publish a Lua library in a short while that will make it quite trivial to add things like Playing Techniques with your own keycommands, and even changing at a whim the items to be created with a key.