- Catholics no longer are required to eat meat on Fridays
- Masses are now ordinarily in the vernacular. Previously they were in Latin.
- Catholics are now permitted to marry Protestants
- Priests were not always celibate
There are others, but I think these will suffice to prove my point. First, we must examine what is entailed in Papal Infallibility. Simply put, when the post is exercising his authority as the pastor of the Universal Church, he is making a solemn definition, and he is teaching on faith and morals, the Pope speaks infallibly. Furthermore when the College of Bishops are in agreement with each other, in communion with the Pope, and are making a declaration on faith and morals, they are likewise speaking infallibly. With these restrictions, infallible statements are fairly rare. In all of the 20th century, the only infallible statements made were the documents of Vatican 2, insofar as the statements made on faith and morals, and the definition of Mary's Assumption into heaven.
The rarity of infallible statements notwithstanding, there are further distinctions to be made. First is that a line must be drawn between "doctrine" and "discipline." Clerical celibacy is a discipline. Abstinence from meat is a discipline. The language of the liturgy is discipline. (As a side note, if the Church would require abstinence of meat on Fridays, the sin would not be consuming meat, but failing to submit to legitimate authority.) Doctrine is an absolute teaching in faith or morals: The Mass is both a meal and a sacrifice. Abortion is an intrinsic evil. Artificial means of contraception are not to be practiced. Remarriage after divorce is unacceptable. Mary is the Mother of God. The Scriptures were written under the inspiration of the Holy Spirit.
The distinction is clear: Doctrine is what we believe; practice is how we respond to that belief. With this distinction in mind, it becomes clear that doctrine has not changed, but our practice most certainly has.