Can I put satin ribbon on the bottom tiers of Crusting BC frosting?
Yep, but you need to put a barrier between the ribbon and the buttercream or the grease will soak into your ribbon. I use wax paper. I just cut a strip of wax paper the size of my ribbon and put the wax paper "ribbon" on the cake first and attach the ends with a piece of tape. Then I put the ribbon over the wax paper and attach the ends with a pretty corsage pin or two. I like doing it this way because it's easy to remove for cutting.
Some use water to saturate the ribbon so that grease spots don't show. I don't like doing this because it can change the color of the ribbon by making it appear darker.