I don’t know if anyone has discovered this yet. It’s not merging, but today I realized that from the back end I can delete a customer from an order and assign a new one. A little bit longer than doing a “simple” merge, but it definitely solves the problem of having multiple accounts. You can just delete whatever order went under the wrong name, or alternate name, and reassign to the one you’d like to use.
I hope this helps, I got so excited when I realized this!