Thanks for the update Simon, sounds good! Yeah I remember running into the rate limiting with this before I realized those limits existed, I subsequently spaced out the requests and it worked from that point forward but too late in this particular case 
Sure if you have a username fixer script handy I’d be glad to give that a try. Sounds like the username thing won’t have much material impact but I may as well try fixing them now while they mostly haven’t been active yet, try to eliminate any potential source of confusion.
Will stay tuned for the next WP Discourse update!