Go to Tool > Preferences... > Editing > Shortcuts and click New. That pops up a dialog to create a new shortcut. In the Function: field, enter 'buffer-view pdf2' to view, 'buffer-update pdf2' to update the view or 'buffer-export pdf2' to export (omit the quotes). Then click in the empty Shortcut: field and press the key combination you want to assign. (I'm describing the dialog as it appears in Windows, but I imagine it's the same on a Mac.) The key combination will be displayed in the field. Click OK. If the key combination is already in use, LyX will nag you to remove the current assignment before reassigning. Once your combination has been accepted, I suggest you click Apply, test it, then come back and click Save to store it.
It might be a good idea to first copy your bind file to your local settings directory, select the local copy as your bind file, and then modify it. That way, if you upgrade or reinstall, you don't lose the customized bindings. /Paul
