It's a 3g/4g connection and not wifi or wired internet. This plus how they describe its use leads me to think the stories are all on their server and sent on demand when they are requested through that always-on connection. It's the same as how old kindles offered a 3g connection that was always on.

I'm assuming it's not easy to get in the middle of that connection so I would probably try the server instead. You could try to social engineer the password from someone who owns the machine, and if that doesn't work you would try to find an exploit in the admin portal, which could be very easy or very hard. There are resources and tools online if you want to learn how to do that.

It looks like it may be easier to remove the ink and replace the printer roll.

Hacking in what sense?

An invention for

Physical access, it has some storage medium that has the stories, then just find a way to edit those stored stories. Regular Expressions are a possible option to replace common phrases with racist ones.