I want to make a special box of cookies for someone who has really been very helpful and kind to me. I am making cookies covered with cornflower blue fondant. I will be doing the white design on the fondant with RI. I also want to dust the blue fondant with pearl or luster dust. Can I do that before the RI goes on or will the pearl dust keep the RI from sticking to the fondant? Thanks for your help.

You can do it before - the RI should be "wet" enough that there shouldn't be any problems with sticking.