Hello Charles,
That Hauptwerk v3 user guide did indeed have a list of the computer key codes that you could assign manually to trigger menu functions (or other things), but in v4 you can instead simply auto-detect the keys to the desired menu functions via the 'General settings | Advanced ... | MIDI/key triggers for loading organs and other global menu functions' or 'Organ settings | MIDI/key triggers for master pistons and menu functions' screens. You can also see the list of supported computer key codes on those screens if you set the 'Input' setting to 'Computer key'.
In that way it's possible to configure most menu functions to be triggered from computer keys (or MIDI pistons, etc.), but not functions that would require browsing for files, and currently not, I'm afraid, menu functions that open/close any settings screens or control panels.