If the Catholic church is the “true church” why would they have to change anything? It would be pure like Christ, and nothing would need changing. Reform does mean change, doesn’t it?
The deposit of faith does not change and cannot change. Things that can change, and sometimes need to change are how the Church responds to the changed world. For example, when the Church became powerful and wealthy in the Middle Ages, the emphasis on monasticism and self-giving became needed and St. Fransis supplied it. When the Protestant Reformation happened, the doctrines they questioned needed to be clarified and we had the Council of Trent. When materialism ans secularism became the force of the day, we had Vatican I and the wrok of Leo XIII. When Latin stopped being universally recognized language, worship in the vernacular languages had to develop and we had Vatican II. Now we have a sexual revolution and its evil fruit; this necessitated developemnt of theology of the body that uphold the biblical values.