WarcraftRealms.com

I tried to register for this site, forgetting that I already had a username I haven't accessed in years.

I don't really use this handle anymore and haven't in many years, a lot has changed in my life since then and I'm a completely different person.

Would it be possible to rename this account to that other name (and delete that name)?

Sorry without an active Administrator with full access to system level DB tools that modification is impossible.

At this time with no active administrator, starting new accounts is also not going to happen.

And I have no clue if or when Metalbeast will assign a new administrator for this site.

Look at the Private Message (PM) I sent you.
I believe you got very lucky.. even if it wasn't what you requested.