You do not need anything complicated to search the game files. Just "find in files" in Notepad ++ (and select the Stellaris common and events folders). As for what you do, you want to set up an event on_game_start (so you make an on_action entry on that on_action to trigger your event) and then copy one of the Vanilla events on_game_start, rename it (to what you set to trigger in the on_action) and edit it to make the event do what cray says.