Most Rolex backs are steel and cut very well. But I did a little research and it seems the Rolex deep sea new models have a grade 5 titanium back plate. Then I read a little about the Grade 5 titanium and it seems like real tough stuff.
I haven't cut a new rolex in a while, just vintage rolexes. But I was told that in the last few years they moved from the easier to cut steel to something called oystersteel, a proprietary blend, which I am told is a bit tougher and more corrosion resistant.
The problem with the rolex deepsea back is if it doesn't cut well, where will you find another back plate to replace it? Even if the engraving cut could be sanded down, will the owner notice?
Kind of gives me a big pile of pause to even think about doing it. The only way around this is to bump up the responsibility to either the watch owner or the store owner. If they insist on it being engraved, have them sign a release of responsibility. And if they accept responsibility also let them know that even if things go wrong, they have to pay you for your time in attempting it.
If it sounds like I'm getting carried away, the rolex lists for 12,500 US dollars. That's a lot of dollars. This is one of those situations where a lot of dollars could translate into a lot of aggravation. A lot of aggravation.