Although moderators [2] (and users, if permitted) [3] are able to modify their usernames, I’ve no registrations at instances which permit this, likely because of disadvantages similar to those described at t/62451/6, so I am unable to confirm. However, at least that disadvantage shouldn’t apply to this type of rename, so should it be permissible?
At t/164553, I see that Discourse appears to treat usernames in a case-insensitive manner, but definitely retains the original case.