Can I

place a Royal Icing runout decoration on an Italian Meringue butter creamed cake.  Or will the fat in the BC melt the design.

It will be fine.  Just make sure your sugar work is dry before moving to the cake so it doesn't break when handling.

Thanks for your quick response.  I will place them on the cake tomorrow and cross my fingers, although I've never been steered wrong in this forum. :o)

AIt'll be fine [B]for a few hours[/B]. After that the fat will begin to breakdown your ri. You can place them at the last minute or give your run outs a fondant backing.