use_boxcox was set at model initialization and cannot be changed

Raise code

DO: Deprecate initial_level and related parameters from fit
        if initial_level is not None or initial_trend is not None:
            raise ValueError(
                "Initial values were set during model construction. These "
                "cannot be changed during fit."
            )
        if use_boxcox is not None:
            raise ValueError(
                "use_boxcox was set at model initialization and cannot "
                "be changed"
            )
        elif self._use_boxcox is None:
            use_boxcox = False
        else:
            use_boxcox = self._use_boxcox

        if