You can just google Game Dev Tycoon Modding and there's a Greenheart games github page explaining how it works. You'd need to know some javascript, although it's not hard to learn that especially if you look at their example mods and have low expectations. I'm tempted to make a mod too, so I looked into it and it seemed doable, but I didn't really have any cool ideas for mods. Most people just want to add a new this or that but with a certain name and picture without changing the way the game works at all. A new console or genre. You want to add a few topics so this would be very easy because you can just copy an example for a new topic and then change some text and numbers. But that would be a good way to get into it, then maybe you'd be open to learning how to do more. It's still the same game, just with new topics and stuff. Nobody
seems to replace the actual mechanics of the game or the process of developing games.