But to consider the rules of morality as improvable, is one thing; to pass over the intermediate generalisations entirely, and endeavour to test each individual action directly by the first principle, is another. It is a strange notion that the acknowledgment of a first principle is inconsistent with the admission of secondary ones. To inform a traveller respecting the place of his ultimate destination, is not to forbid the use of landmarks and direction-posts on the way. [Utilitarianism, Chapter 2]
Mill here almost seems to concede the possibility that utilitarianism is not a “first principle” but closer to a moral strategy.