Here is what I want to do:

1.) Highlight desired notes in Key Editor. 2.) Press Keyswitch on piano keyboard that matches expression map. 3.) Have those notes be assigned that articulation.

Not quite sure why I'm having so much trouble with achieving this (or if it is even possible) so any help would be greatly appreciated.

 

To apply articulations, you have to load an expressionmap in expressionmap setup, show controllers lanes in lower window in key editor and open "Articulations". Then you write articulations one by one by opt_click (or alt_click) at cursor position.