Hi there!
You can contact a mod by starting a conversation with any mods on forums. For the list of current mods, click
here
You can buy fikicoins using the Mice Arena android app! Otherwise, you can't change your username. However, I'm afraid that the app is currently not available until the new one is published! Do take note that you will need to purchase fikicoins will real money
(P.s feel free to correct me if I made a mistake^)