No, that isn't how it works - the names can be set from text and then they are ok for the entirety of the game. You are setting the name from text using an operation that was only used originally in the debug menu. You can choose when to use it. Just before getting Cait and Vincent, you'd use it.
If you take the time to use that function in each and every field, that's exactly how it works.
I know which function you are referring to, I've used it many times. In that context, when you say you can choose when to use it is also what I meant in my previous post. If you want Cloud to be called, for example, John in one field and Elizabeth in the next, it is possible with this.
@sithlord
I don't suppose you'd be able to tell me how make the field script force the character ID to change, then? Because the Create/Delete character opcode, which is commonly used to make characters available, is definitely not what activates the ID change.