This patch implements a new message box system that allows for messages of 260 characters (almost twice the original length). It also makes it possible to use more than two different messages per (trans)level, giving each screen its own message settings.
README.txt and HOW_TO_USE.txt will probably answer any question you may have, so give it a read.
(July 7, 2018: Made switch palace messages work, tweaked the message system to be more space-efficient, and made other minor improvements.)
(July 7, 2019: Fixed broken SA-1 compatibility and added support for LM 3's new level sizes.)