I finally found the answer - select a string patch.Go into the channel strip,click the EXS instrument button until the plugin window opens.Click the display where the instrument name is shown.This gIves a drop down of the instruments.under strings, all the articulations are there.Pick the one you want to use.Close the plugin.Your patch will now have the articulation selected,and it keeps it after closing..Auto save/Save of course.
Ignore the buttons in the main window - they are for mapping soft keys on your controller,if like me you want the patch for stage musicals ,theres no time to adjust so the settings have to be saved in your patch list.I am a raw beginner with MainStage,there doesn't seem much on the net about this.
Hope this helps anyone struggling like I did!