My old main was Dhankx

My new main is Rheck

Is there a mechanism (keep in mind I'm GM too so) where all of my data on the website that says Dhankx can be changed to Rheck? Including my login account name?

Sure, all you have to do to rename is go to "Edit my Account profile" in the "Logged In" box, and you can rename your account there.

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It's all in the reflexes.

Thank you, now how do I get the name in the raid standings to be switched?

From Dhankx to Rheck?

If I understand what your asking for in this second part correctly just go to Admin and under the DKP stuff is a link to do a Full DKP Transfer and thus transfer DKP from Dhankx to Rheck.

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Six Demon Bag
Jack Burton: Hey, what more can a guy ask for?
Egg Shen: Oh, a six-demon bag!
Jack Burton: Terrific, a six-demon bag. Sensational. What's in it, Egg?
Egg Shen: Wind, fire, all that kind of thing!

Of if you just had the name of your character changed, you can Edit the name of your character by clicking on it in your "Logged In" box, clicking "Edit" on that page, and then changing the name there.

Or Admin > Characters and change the name there

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It's all in the reflexes.