I am pretty sure I read somewhere on this website that this model has the ability to change the messages by putting the messages on an SD card.
What the message lacked was the filename(s), size of SD card supported (it may be 1GB or less and FAT format like the iViews), or the contents of the file(s) and formatting of the text (?) within.
I'd pay someone for that info..,.,... "...it contains information proprietary to the property.." Well, then take that info out for us, randomize it.

I do wonder how they programmed these, though, in mass quantities .. Not much info on the MC300 for some reason.