Anything can damage chrome. Nevr-Dull, like any other product, can scratch chrome if there is sediment in the fabric. It picks some up as you scrub off contaminants (i.e. exhaust soot). Pressing hard can cause the sediment to make very fine scratches in the chrome. I've never had it scratch chrome because I always clean the chrome first and use fresh Nevr-Dull, turning it often. Used correctly, that stuff is pure magic!

 

Any dust will scratch chrome so just be careful. And your decel popping is probably coming from the exhaust leak.

 

If you rub it with a finger, when the exhaust is cold, it will be easy to tell if it is exhaust soot or a boot scuff. The boot scuff will be hard and immovable, while soot will dirty your finger.