I'm pretty sure that's not allowed. It would be a serious security breach if js
could get to that part of Windows. The best you can do is self.print() and let the user change the printer settings when the printer dialog box comes up.
You could pop-up a little message window just before calling self.print() that would advise the user as to the correct printer settings. However, the main window may come back to the front and obscure your pop-up, so open your popup with a specific window name (like MsgWin), then after self.print() try coding MsgWin.focus().
This is sort of off the top of my head...