I have used royal icing decorations on IMBC and even refrigerated and brought to room temperature with no problems. I think royal icing tends to absorb the Crisco in standard powdered sugar buttercream, but it doesn't do that as much with IMBC and butter. I find that to be true with wrapping a cake in ribbon as well. Crisco icing soaks into the fabric of the ribbon immediately, darkens and changes color. I don't have that problem with IMBC, but I do stay away from all satin ribbon.
I'm not sure what IMBC is, but I've used Royal on regular BC and it works great. The only problem I've had is that the Royal breaks very easily ontop of the soft BC. I think that alot of your snowflakes are going to break with the first slice of the cake unless they're pretty thick. Hope this helps!
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