Should I use royal icing and pipe directly on the crusted buttercream? I have done this before with black buttercream but I have to make this cake a little further ahead then I usually do and worried the black will bleed. Suggestions?
Thanks!

I just did an experiment with this, and as long as you pipe on crusted buttercream and keep the cake cold it should be fine. I used buttercream, not royal. Started with cocoa in it then added black food coloring, then more cocoa if it got too soft.