The message text limit for the Marquee screen saver is 255, even if you bypass the dialog box that prevents you from entering more than 255 characters
If you find an old Windows XP machine and fire up the configuration dialog for the Marquee screen saver, you’ll see that the text field for entering the message won’t let you type more than 255 characters. That’s because the Marquee screen saver uses a 255-character buffer to hold the message, and the dialog box figure there’s no point in letting you type in a message longer than the screen saver can display. A customer decided to bypass the configuration dialog and change the text in the screen saver by editing the settings directly, and then complained that the Marquee screen saver truncated the message at 255 characters. Well, yeah, because the limit is 255 characters. That’s what the dialog box was trying to tell you. If you bypass the dialog box and whack the setting directly, that doesn’t change the Marquee screen saver. Its limit is still 255 characters.
It’s like attaching a gizmo to the gas pump fuel nozzle to disable the auto-stop feature because you want to put 20 gallons of gas into your 15-gallon tank. Disabling the auto-stop will not make the gas tank any bigger. All it does it make it easier to accidentally overflow your gas tank’s buffer.