Yes, I trim while in the mold. Making them really is not a long process, the coloring was. I kinda went overboard with the colors, but I was so worried about not having enough natural hues for the variety of shells. I even used light blue, coral, peach, antique white, antique gold, super gold, silver, charcoal.... my daughter kinda thought I went a little nuts.
buuuut, I like how they turned out.... the next time I have to make some I am sure I will use just the core 5 colors and super pearl.
Being fondant they not only had the look but the feel of real.