BitcoinTalk Profile Guide

[DdmrDdmr]

Is it possible to edit one's username and email used during registration?

Don’t you mean after registering?

During: Yes, you can choose your username (providing it is not already taken) and add your email.
After: No, you may not edit your username(*), but you can change your email.

There are very few exceptions to this, such as becoming a VIP (and cashing our 50 BTCs in the event).