The Pope can change Catholic doctrine, just not all at once. He and his priests have to do it brick by brick, and it can take decades or centuries, but it happens. I believe either Mary’s “Immaculate Conception” or her “perpetual virginity” was established this way (or quite possibly both). First introduce the idea as possibility, speculate on it, and then many years later when people have grown used to the idea (that is, it’s taken root), then declare it dogma.
nope
For one example, look at the “Immaculate Conception” of Mary. It went from being an open question, with the Catholic Church refusing to take a position on it, to a dogma over some centuries. And from reading the Bible and especially the Gospels, and then the New Testament, it’s clear the Mary was in no way any sort of object to be focused on. Jesu Himself addressed her as Woman, and when given the opportunity to hold her up publicly (when a woman referred to her in blessing who breastfed Him) He didn’t, not even partly, which would have been to agree then change the focus. Instead, he corrected the woman and changed the focus.
Next up is Mary as a co-redemtrix as official dogma.
In the early 1990s Professor Mark Miravalle of the Franciscan University of Steubenville and author of the book Mary: Coredemptrix, Mediatrix, Advocate launched a popular petition to urge Pope John Paul II to use Papal infallibility to declare Mary as Co-Redemptrix. More than six million signatures were gathered from 148 countries, including those of Mother Teresa of Calcutta, Cardinal John O'Connor of New York, and 41 other cardinals and 550 bishops.
In August 1996, a Mariological Congress was held in Czestochowa, Poland, where a commission was established in response to a request of the Holy See. The congress sought the opinion of scholars present there regarding the possibility of proposing a fifth Marian dogma on Mary as Co-Redemptrix, Mediatrix and Advocate. The commission unanimously declared that it was not opportune, voting 23-0 against the proposed dogma.
By 1998 it was doubtful the Vatican was going to consider new Marian dogmas. The papal spokesman stated "This is not under study by the Holy Father nor by any Vatican congregation or commission". A leading Mariologist stated the petition was "theologically inadequate, historically a mistake, pastorally imprudent and ecumenically unacceptable". Pope John Paul II cautioned against "all false exaggeration", his teaching and devotion to Mary has strictly been "exalting Mary as the first among believers but concentrating all faith on the Triune God and giving primacy to Christ." When asked in an interview in 2000 whether the Church would go along with the desire to solemnly define Mary as Co-redemptrix, (the then) Cardinal Ratzinger responded that,
the formula “Co-redemptrix” departs to too great an extent from the language of Scripture and of the Fathers and therefore gives rise to misunderstandings...Everything comes from Him [Christ], as the Letter to the Ephesians and the Letter to the Colossians, in particular, tell us; Mary, too, is everything she is through Him. The word “Co-redemptrix” would obscure this origin. A correct intention being expressed in the wrong way.