since it's plating it may cover the engraving, but i don't know Depending on what the material is now, it may change the sound

ok, playing dosn't cover up anything. It will show ANY scratch or engraving. what will change it is the buffing they "will" have to do to remove said scratches, which may interfear with your engraving. My 10M for example is like this, and some of my engraving is hard to see. I doubt it will change the sound too much, since you really aren't adding a lot of metal. 1oz of gold is like 475 (or something) and I doubt they would use a lot more than one. ps, brushed gold/silver is awesome! and combine that with polish and you got a great horn!