I'm trying to remember if I've ever done that. I have occasionally mass-changed a proper name in revisions, but I don't know if it was for that reason. And you have to be careful that the name you're replacing doesn't appear as part of a word in the document, like, say, "Simon" in "parsimonious" (or else that you have your search function set to be case-sensitive). I had that happen just recently (can't remember what the name was), but I caught it in time.
This is true. If you're placeholder name is "Bob" or "Sam," you're just asking for trouble.
In which case, instead of of doing a global search-and-replace, you should probably take the time to do the s&r thing case by case . . ..