I noticed that the 2012 version of 70E indicates that opening troughs has a significant arc flash and perhaps shock hazard, which is something I never considered before. Does anyone else have any specific safety rules for this? What would be the safety risk from doing this activity?

Are they talking Wireways or Splitters? With a splitter there could be the chance of something falling into it or accidental contact, if the installer was nice enough to mount the hinge on the top... With a wireway, unless you close the door on a wire, don't see it and continue to force it closed causing it to short out there shouldn't be much of a hazzard.. In my opinion...

I could see a higher arc flash hazzard with a splitter, but not sure on a wire way...