Is it possible to have the username changed but attached to the same account?  I have been a member since 2000 but wish to have my username (and display name if different) changed to reflect what I use on all other sites that I frequent.  I know I could just create a new account, but I don't want to abandon this one from 2000.

You should be able to change it in your profile settings:

https://www.gamedev.net/settings/username/

thanks.  taken care of.

any way to change the username used for login as well?

I don't believe that can be changed unfortunately.