and to offer another option, you can do this using the OSX built-in Keyboard Preferences > Shortcuts feature.
Select App Shortcuts and click on the [+] button. Set the Menu Title to "Save as PDF..." (yes it works with 3 periods as well as the ellipsis) and set the keyboard shortcut as you wish.
I prefer ⌘S as this shortcut. Since this menu item only appears in the print dialog, there isn't a conflict with the typical ⌘S shortcut for Save because the File menu is unavailable/disabled when the print dialog is in front.
P.S. I just noticed on my High Sierra system, the ellipsis is no longer in the menu title.