I'd be more worried if the engraving process got into the circuitry or shook the hard drive to death. Once it is out of warranty, you may want to learn from
http://www.ifixit.com/ how to carefully remove the shell, and engrave it separately. Any engraving process is likely to be obvious and give at least some eyes a hard time to turn the other way, if the machine has to be brought in for repair.