Create an Out of Character account.
Once you've created your character, create another account with the name of your choice to act as your OoC Account.
Link your OoC account to your character account(s).
Go to your User Control Panel and click "Link Account". Fill in the credentials of the account(s) you want to link to.
You can now switch between accounts without having to type anything in.
To switch accounts, click on your account name on the top right corner of the forum and select the other account from the dropdown menu.
You can post as another account without having to log off.
Underneath the textbox where you draft your posts, there is a "Posting as" option. Select your character account from the dropdown menu.