I wonder if there was a way to get the dumbing down to actually make the player appear dumber without having to rewrite all the texts of the game.
You can make the dialogue the main character says go through a dumbing down filter. Adding verbal ticks like adding dude or bro at the start or end of sentences, adding "like" in a lot of places, adding "you know what I mean". Replacing complicated words with simpler ones, perhaps by adding a four- or three-syllable limit working off a dictionary. Perhaps a bit too complex to make a good automatic filter.
That all just demonstrate that the character is dumb. I would like something that makes the reader/player feel dumb somehow...