I'm sure this has been addressed already, but I'll ask anyways. Can you airbrush on buttercream covered cakes? TIA!

Yes. Just about anything will take airbrush. Although if you spray a lot, it might bead up a bit.

Be sure to hold airbrush away from cake. If too close, can blow the icing up ,etc. Mike Terry demos this all the time at the ices convention. He uses the pearl sheen spray. Just gorgeous.