Play full orchestral score while changing or adding a single note

I've been working with version 4 for a couple weeks now. I can't figure out how to get all notes for all parts to play while I'm adjusting a single note. The objective is to be able to adjust a single note in the entire score (vertically) and listen to how it changes the harmonies and interplay of all the notes from all the other instruments all in the "vertical". To keep it simple, take a piano score. Say I have a cmaj triad, but I want to change the e to e-flat. I want to be able to hear the triad change from a c maj to a c min when I drop the e to eflat.... AS I change it without having to go into play mode... same goes for an entire orchestral score...