I missed this thread totally 

Diamond coat is just another word for clearcoat. It is supposed to be the most durable CC.

Most Bally/WMS games also have Mylar in high traffic areas - Like TAF has some around the scoops, Fishtales around the ball drop areas. This can be removed using several methods. The Hair Dryer method should be ok for mylar on Diamond Coat.

Just try a test spot first. Insert lettering lifting is a risk and there's no guarantee that it will work. MartyJ has done this and also applied some new insert decals to great effect.