1- If you plug in your own blueprints instead of existing ones, expect everything to get broken. There’s a lot of links between various BPs, and they immediately get broken when you replace them. Think of placing the electronics of a Boeing into a Airbus. Why would they work, if it’s completely different planes? Obviously, you can adapt them, but it requires a lot of work.
And you could make child BPs inherit from the same class, but in-game classes do not warrant such drastic measures.
2- The way to make different in-game classes (rogue, warrior, etc) is not by making different blueprints for each class. You should make a replicated enum (for your in-game class) on the Player State BP, and depending on its value, the model may change or other changes may take effect, depending on what different classes entail in your game.
You should set this value in OnGetCharacter, and you should add the retrieval of this value in the associated php script.