No, you don’t have to scroll all the way to the top of the thread. Go to your browser bar–it’s at the very top of your screen and the place where you would type in a web address. Directly underneath that will be the web page itself. At the very top of the webpage will be a small bar that reads something like this:
Forums > World’s End Tavern: Role-play and Fan Fiction > (name of thread)
Directly to the right of that label is a small symbol of a magnifying glass paired with a small portrait of your character. Clicking this portrait will open a drop-down menu that will have a Change Character option. Clicking this option will bring up a larger window full of portraits of all your toons. Simply pick which one you wish to post on and the box will close, thus changing your character. Rinse and repeat every time you want to switch.