Ninzalo

В итоге, своими силами получилось нечто такое:

class Main_key:
    def __init__(self, outer) -> None:
        self.outer = outer

    def change_main_key(self, main_key: str):
        if not self.outer.main_key:
            error_str = f"Outer class don't have .main_key param"
            raise Exception(error_str)
        old_main_key = self.outer.main_key
        self.outer.main_key = main_key
        print(
            f"Main key '{old_main_key}' was changed to '{self.outer.main_key}'"
        )


class Keys:
    def __init__(self, outer) -> None:
        self.outer = outer

    def add_key(self, key: str | List[str]):
        if isinstance(key, list):
            for k in key:
                self.append_keys(key=k)
            return
        if key in self.outer.keys:
            error_str = f"Key value '{key}' already exists: {self.outer.keys}"
            raise ValueError(error_str)
        self.outer.keys.append(key)
        print(f"Keys list was appended by {key}")


@dataclass()
class My_class:
    main_key: str = "type"
    keys: List[str] = field(default_factory=list)
    main_key_funcs: Main_key | None = None
    keys_funcs: Keys | None = None

    def get(self):
        self.main_key_funcs = Main_key(outer=self)
        self.keys_funcs = Keys(outer=self)


c = My_class()
c.get()
c.main_key_funcs.change_main_key(main_key="subtype")
c.keys_funcs.add_key('first_key')
c.keys_funcs.add_key('second_key')
print(c)

Работает превосходно, так, как и планировалось

Main key 'type' was changed to 'subtype'
Keys list was appended by first_key
Keys list was appended by second_key
My_class(main_key='subtype', keys=['first_key', 'second_key'], main_key_funcs=<__main__.Main_key object at 0x102acd1d0>, keys_funcs=<__main__.Keys object at 0x102acd250>)

Можно ли как-то улучшить? Открыт к предложениям