I've seen a lot of very pretty cakes with rhinestone trimming added to them.
Some around the base and some diagonally and across the middles.
How would this get attached to the cake? Do you try to wash them before adding?
I wash and sanitize it and then attach it to the base of the tiers with washed and sanitized T pins. And tell the caterer to count the pins as they take the trim off. (And how many pins there are.)