I would assume it would work. If you haven't tried yet, and no one answered you, maybe you could PM her- she may have tried!
i myself have not done it, BUT i have read in a colette peters book on techniques where she airbrushes royal icing decorations that have dried. i would suggest that you allow at LEAST 24 hours for the icing to dry before you decorate, otherwise the color may cause the icing to melt since the colors are water based. are you planning on using regular airbrush colors or alcohol and luster dust? if you do silver dust w/ alcohol, that will evaporate quicker so as not to melt the icing, i've done that on fondant cookies.
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