For the most part, keyboard commands are fairly consistent throughout Photo Mechanic. We can tag/untag a photo with T and set color class with 0,1-8 in a contact sheet, the preview window or during a slide show. However, for the star rating of a photo, Alt-0...Alt-5 can be used in a contact sheet or the preview window, but it does not workduring a slide show.
Also, while Alt-0...Alt-5 can be used with the preview window to set the star rating, a beep is generated when the key is pressed (at least in the Windows version).
-Ian