When you change your display name, everyone will see your username as that. The only difference is that when someone visits your profile, the profile link will remain as http://mydramalist.com/profile/Samy .
I don't like that it has no delete account feature plus you can't change your username. I registered with my Google+ account, then after that, I found out that I can't change my username which is automatically assigned by your website.
I want to delete my account because I can't change my username. Sadly, deletion of account is not available also. I can't. This website gets 0/10 for privacy.