using icing with buttercream to write with I am decorating a cookie for a wedding and packing them separate in a clear bag for a thank you gift.  I've used the instructions from the meringue container for icing but wanted to know if I could use butter cream with real butter, add the meringue powder and have crust up so the writing doesn't smear in the package but taste better than plain icing.
I wouldn't suggest using buttercream icing- even if you add meringue powder to it, I don't think it will get as hard as you'll need it to prevent it from being ruined when put inside the bags. I always use royal icing with meringue for my icing (this recipe, specifically) and I think it tastes great.