during the migration process you might have received an invitation email with a prefilled, system chosen username which might not be your favourite one. Unfortunately you weren’t able to change the username yourself.
We now reactivated this feature so you can change your username yourself for a grace period of five days after your registration. This is limited because all mentions (and some other links) are broken after changing the username (see https://meta.discourse.org/t/how-to-enable-users-to-change-their-username/19186/3 for a detailed discussion about this topic).
Enjoy the new openHAB community,