I do modeling chocolate on cookies all the time. It tastes delicious, very milld, so the flavor of the cookie really shines through, and is easy to do. Here are a few I've done:
I roll out my modeling chocolate with the 3/16 ring on my pin, and then cut out the shapes with the same cutter I am planning on using for the cookies. I set those aside, and then make the cookies. As they come out of the oven, lay the modeling chocolate cut outs on top of the hot cookies. The modeling chocolate will get shiny and melty and adhere to the cookie. While it's melty, you can stick on decorations, such as the premade royal icing flowers you see on the shoes and wedding cookies. Let them cool completely, and then you can add on piped royal icing decorations, like the leaves on the wedding cookies and pumpkins, or impress the cookies, like I did to create the lines on the pumpkin cookies using the rim of a cup. On the wedding cookies, I used a brand new clean stamp, that I ran through the dishwasher, painted with Americolor black food gel to stamp the bride and groom on. The cookies can then be individually wrapped or stacked.
The pumpkin cookies are made with pumpkin pie spice and part brown sugar, so they taste just like pumpkin pie to eat! The wedding cookies have orange zest in them. I like modeling chocolate better than fondant on the cookies... The texture is not chewy, like fondant is, and it's less sweet.