Phrases in the Registration Page: How to change the wording of the "Username" field for end users

Hi 

We want to change the “Username” in our registration page to “Public Username”. So our End Users are aware that their username is public. (They sometimes use their real name and then request to change it for privacy reasons, so we want to make it clearer from the start.)
Which hidden phrase can we use in order to change the wording of the field “Username”?

I read this article and tried the hidden phrase mentioned there but it didn’t work because i’m not using the SSO Page, instead we use the regular Login.