Given the time pressure (and to a lesser extent, the dye and chocolate
limitations) I'd suggest supplying already baked cookies, and having them
decorate them.

If someone at the school is insisting on baking...there are hard gold and
silver candies meant to be baked on, those little red hot candies, food
coloring mixed in dough, sprinkles (both the sparkly large sugar crystal
kind and the tube shaped kind.) Even the sprinkle discs might not melt.
Chocolate chips and kisses will melt, you might want to pull the cookies out
when they are almost done to put those on. M&Ms, and all their derivatives
won't melt as long as the candy coating is intact, so you could decorate
with them.

Years ago I remember making "stained glass" cookies that used life savers
melted in the middle to make a see through center. But I don't rememer that
recipe...