I'm a staff member but I don't have all of my permissions yet so contact Jeff Westover or Minta for help - if you go up to the little person (head and shoulders) icon in the brown bar at the top of the page, select Conversations from the options and type your message for them. They are volunteers so it may take a little while to get back to you. You can also select the Signature option there and make a note in your signature line until they can help change your user name. For example, you can sign yourself as "Holidayhelpelf soon to be (enter whatever your name will be here)".
I would also like to change my user name but when you go to conversations - do you address it to one of the specific people you mention? Not sure how this works...