If only a one-time amendment could be allowed, that would be sufficient ( Arsalan Shah)
We thank you for your great efforts ( ~Z~ Man)
I don't think there is much problem in editing username but in fact there are some components like mentions, display users and other things, when username is used somewhere. So in general username editing is not allowed. But maybe we set a flag to allow editing of username only one time.
Thank you very much for your feedback, Naser.
I will keep your idea in mind and talk to Arsalan if it wouldn't be possible to allow username editing in general.