With many ketches the mizzen is set so that a large portion of the mizzen boom hangs over the stern. When I look at that I wonder how you arre supposed to get to the mizzen clew, especially at sea. Also access is needed for fitting sail covers, etc. I certainly would not be hanging precariously out over the wake in the ocean. IMHO that would be suicidal if you are single handed.

So, experts, how is it done safely? Lower the sail and un-ship the gooseneck? Hoist the boom vertical and then climb the mizzen mast?

you don't need to get to the clew at sea reefing lines return to the mast covers go on on the dock you may as well ask how you access the clew on a cruising cat with the boom miles off the deck behind the canvas roof