Yes, you can use the molds. If your molds happen to have little feautures on them like dots etc. You can melt your choc. put it in small pastry bag or plastic baggie with a small tip, pipe that color on, wait for it become firm and then fill your mold.Use candy melts. If you use real choc. then you will have to temper it. Hope this helps.
a mold is easier. You could also draw a butterfly and then pipe it out on waxed or parchment paper and then carefully place it on your cake.
I did hundreds of these for cupcakes. It works great if you have a template on your computer to copy multiples on a page. cover the page with waxed paper. Do the outlines of the butterfly in one color and fill in the wings in others. Or trace and fill with filligree lines.
If you do the wings separately you can just insert them in the icing and pipe a body.
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