I would like to use the Guitar model in "piano mode" rather than as a guitar emulation. YJe preset 'Guitar à la piano' is for this purpose but I can't find the Casual/ Pro setting in it, so I'm unable to turn off the string sweeps and the annoying "casual" guitarists' noises. How can this be done?

You can still switch temporarily to guitar mode by clicking twice on the 'C' button in the top left corner of the keyboard. Then move the slider to 'pro' and click again on the button to return to the piano mode. Not very convenient, but it works !