The µTune can not add or subtract notes via button push, mostly because it does not have dedicated buttons for this. You can however use a CV-in to transpose.
You can of course use 12TET, it is even the default scale after startup
I don’t know very much about max msp and how it interfaces with the world. If MAX msp can send midi, then µTune can receive and output this. Currently you could use note and/or pitch bend commands for this, midi controller messages will be supported in the upcoming update as well.