200 years old? 500? Does an actual grave marking the spot make it any more or less acceptable to examine remains? Where's the line, whether contextually or age-wise?
If there's a better subreddit to ask this question, I apologize in advance.
We had a quite lively discussion on this very topic about a year ago.
If you ask r/archaeology, you'll be able to get some better answers, as they'll be folks actually doing the disturbing.