You can't change the 'permissions' a new player that is joining your world is assigned with after creating the world.

This isn't really a bug but more of a request to improve the Quality of life. When creating a New World you can set it so everyone that joins is automatically given the 'member' role or 'visitor', but after creating the world there is NO way to change this, for example when you create your world and make it so everyone that join is a 'moderator' but you later decide that you want to change it to 'visitor' , you just CANT. You have to manually change the gamemode of everyone that joins your world