From Leo XIII’s Testem benevolentiae:
“The basis of the opinions [which Leo is about to reject] that we have mentioned is established as essentially this: In order that those who dissent may more easily be brought over to Catholic wisdom, the Church should come closer to the humanity of a more mature age and, relaxing her old severity, manifest indulgence toward the beliefs and opinions of the people that have recently been introduced. Moreover, many think that this should be done not only with regard to the standard of living, but even with regard to the doctrines in which the deposit of faith is contained. For, they contend, that it is opportune, to win over those who are in disagreement, if certain topics of doctrine are passed over as of lesser importance or are so softened that they do not retain the same sense as the Church has always held. Now: There is no need of a long discussion… to show with what reprehensible purpose this has been thought out, if only the character and origin of the teaching that the Church hands down are considered.”
Pope Leo XIII rejects the recommendation and notes that the truth the Church hands on is always relevant and that in matters changeable there has always been room for change. Neither doctrine nor morals change!