Does anyone know the ada dental guidelines of tooth contouring and reshaping?

No guidelines. The ada does not publish guidelines for this procedure. It's billing code is called odontoplasty. Is commonly done by dentist to improve function and/or cosmetics. Teeth in bite trauma from tooth grinding/clenching frequently demand odontoplasty to stop bone loss around the tooth. The enamel is important to protect the tooth, too much in the wrong contour must be removed. Purely cosmetic, ?
Common Sense. Tooth contouring and reshaping is always safe and helpful, as long as it's confined to the enamel = the outer layer of the tooth. Thus, the only guideline is to "do no harm." this is easy to adhere to. Slight reshaping and polishing of teeth to make them more attractive is safe, effective, and easy. Like i said, you can only get into trouble if you remove all the enamel, which no one would do.