Hmmm, they don't come with any inside announcements???
If you want to create your own and put them in, then that's a different issue altogether, and I'm unsure if you can alter the config.txt to do it, but, I've never attempted it personally, so, someone more expert on this matter may be able to assist with some info.
Ex-railwayman is right, they don't come with any inside announcements.
Do you mean Destination boards, they only appear at the front, back and sides of the train, to get these, follow the information below, scroll down to the bottom of the page, you will see how the destinations can be placed onto the train.