This is just a theoretical question as I am in planning stage, so I dont need to know how to do things, just if they are possible.
Lets say I have a content type that I need to change and add a required field to. I already have several lists using that content type. What would happen? Would they all be set to a default value? Would nothing happen? Would the creator of the list items be prompted to update the item by filling in the required field?