Sure, you can change the client to connect to another IP, but all you know is what the client sends to the server.

For implementing the server, you'd have to guess what the server will answer.

That is like trying to "reverse engineer" a cocktail from a bar, where all you have is the order you have placed, the drink never arrives because the bar has already shut down.



WoW has private servers because the server files were leaked. I don't know of any game where fans have managed to recreate the server part without any leaked files.