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.)
Added ascii.txt which was missing in this update, added sa-1 tag and added fastROM addressing for long addresses.
If you always had a problem about SMW's message boxes having to few space, this patch certainly helps you, although if even that is too few space, you might want to use RPG Hacker's VWF Messages.
Keep in mind that any sprite and block which sets a message (e.g. Message Box DX) require some tweaks to make them work with the message system (most notably the message number).