Thanks for all the comments, guys! I did my MS helmet over a year ago, and that's long enough to enjoy doing another one all over again.
PROGRESS--Oct 5th:
Killstripes are on.
I masked them all individually with blue painters tape, then painted the "chips" on with masking fluid. I then sponged on Polly S UP Armour Yellow in several light applications until none of the green on the dome showed thru. This is exactly the same technique I used on my MS1. I like to use those really dense makeup sponges. They leave no brush strokes or "dab" marks, and it's a heckuva lot easier than masking everything to airbrush! 
Here she be:
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The next step will be to start mapping/stenciling all the damage on upper cheeks and mandibles. (*gulp*)