You can do this by adding numerous copies of the same text prop into your scene at the exact same location.
Then add the different text to each prop.
Finally use the Show/Hide command (top toolbar) to make each one visible/invisible at the appropriate points on the Timeline.
So for a three Message Board setup you could do the following:
Frame 001: Board 1 Visible, Board 2 Invisible, Board 3 Invisible
Frame 200: Board 1 Invisible, Board 2 Visible, Board 3 Invisible
Frame 400: Board 1 Invisible, Board 2 Invisible, Board 3 Visible
Give it a try to see how it works. :)
Peter
Forum Administrator
www.reallusion.com