In recent discussions with "John" (that's all I know him by) I have insisted that no dogma has ever been changed. He challenged with the teaching on the necessity of the Sacrament of Baptism, and he points to the Ecumenical Council of Florence for the "definition" put forth by that council:
Ecumenical Council of Florence, Session 6, 1439 AD:
With regard to children, since the danger of death is often present and the only remedy available to them is the sacrament of baptism by which they are snatched away from the dominion of the devil and adopted as children of God, it admonishes that sacred baptism is not to be deferred for forty or eighty days or any other period of time in accordance with the usage of some people, but it should be conferred as soon as it conveniently can; and if there is imminent danger of death, the child should be baptized straightaway without any delay, even by a lay man or a woman in the form of the church, if there is no priest, as is contained more fully in the decree on the Armenians.
Also (defining), the souls of those who have incurred no stain of sin whatsoever after baptism, as well as souls who after incurring the stain of sin have been cleansed whether in their bodies or outside their bodies, as was stated above, are straightaway received into heaven and clearly behold the triune God as he is, yet one person more perfectly than another according to the difference of their merits. But the souls of those who depart this life in actual mortal sin, or in original sin alone, go down straightaway to hell to be punished, but with unequal pains.
So, while not exactly the formula we expect from an infallibly defined dogma, this does appear to be a "definition" of the necessity of the Sacrament of Baptism - and those who die without Baptism "go downward straightaway to Hell." Then we come to modern teaching:
CCC 1257 The Lord himself affirms that Baptism is necessary for salvation. He also commands his disciples to proclaim the Gospel to all nations and to baptize them. Baptism is necessary for salvation for those to whom the Gospel has been proclaimed and who have had the possibility of asking for this sacrament. The Church does not know of any means other than Baptism that assures entry into eternal beatitude; this is why she takes care not to neglect the mission she has received from the Lord to see that all who can be baptized are "reborn of water and the Spirit." God has bound salvation to the sacrament of Baptism, but he himself is not bound by his sacraments. http://www.scborromeo.org/ccc/para/1257.htm
Now, before I continue - keep in mind, the Catechism of the Catholic Church is not an infallible document - and NO "catechism" ever has been. That being said, the keys here in the modern teaching are:
a) the Church does not know of any means other than Baptism that assures entry into eternal beatitude and
b) God Himself has bound salvation to the sacrament of Baptism, but He Himself is not bound by His sacraments.
And for another modern teaching:
Again, this commission is not infallible - and is expressing compassion for grieving parents that they MAY have hope in God's mercy. This is not a "change" in the dogma, for even the commission goes on to stress the importance of the Sacrament of Baptism as well as stressing that no one should delay the sacrament from any child. The fact that there is theological speculation on how God MAY have mercy on those whom He chooses does not change the fact that "the Church does not know of any means other than Baptism that assures entry into eternal beatitude."INTERNATIONAL THEOLOGICAL COMMISSION
THE HOPE OF SALVATION FOR INFANTS
WHO DIE WITHOUT BEING BAPTISED
29. The Catholic Church's belief that Baptism is necessary for salvation was powerfully expressed in the Decree for the Jacobites at the Council of Florence in 1442: “There is no other way to come to the aid [of little children] than the sacrament of Baptism by which they are snatched from the power of the devil and adopted as children of God”. This teaching implies a very vivid perception of the divine favour displayed in the sacramental economy instituted by Christ; the Church does not know of any other means which would certainly give little children access to eternal life. However, the Church has also traditionally recognized some substitutions for Baptism of water (which is the sacramental incorporation into the mystery of Christ dead and risen), namely, Baptism of blood (incorporation into Christ by witness of martyrdom for Christ) and Baptism of desire (incorporation into Christ by the desire or longing for sacramental Baptism). During the 20th century, some theologians, developing certain more ancient theological theses, proposed to recognize for little children either some kind of Baptism of blood (by taking into consideration the suffering and death of these infants), or some kind of Baptism of desire (by invoking an “unconscious desire” for Baptism in these infants oriented toward justification, or the desire of the Church). The proposals invoking some kind of Baptism of desire or Baptism of blood, however, involved certain difficulties. On the one hand, the adult's act of desire for Baptism can hardly be attributed to children. The little child is scarcely capable of supplying the fully free and responsible personal act which would constitute a substitution for sacramental Baptism; such a fully free and responsible act is rooted in a judgement of reason and cannot be properly achieved before the human person has reached a sufficient or appropriate use of reason (aetas discretionis: “age of discretion”). On the other hand, it is difficult to understand how the Church could properly “supply” for unbaptised infants. The case of sacramental Baptism, instead, is quite different because sacramental Baptism, administered to infants, obtains grace in virtue of that which is specifically proper to the sacrament as such, that is, the certain gift of regeneration by the power of Christ himself. That is why Pope Pius XII, recalling the importance of sacramental Baptism, explained in the “Allocution to Italian Midwives” in 1951: “The state of grace is absolutely necessary for salvation: without it supernatural happiness, the beatific vision of God, cannot be attained. In an adult an act of love may suffice to obtain him sanctifying grace and so supply for the lack of Baptism; to the child still unborn, or newly born, this way is not open”. This gave rise among theologians to a renewed reflection on the dispositions of infants with respect to the reception of divine grace, on the possibility of an extra-sacramental configuration to Christ, and on the maternal mediation of the Church.
101. “As regards children who have died without Baptism, the Church can only entrust them to the mercy of God, as she does in her funeral rites for them. Indeed, the great mercy of God who desires that all should be saved, and Jesus' tenderness toward children which caused him to say: ‘Let the children come to me, do not hinder them’ (Mk 10:14; cf.1Tim 2:4), allow us to hope that there is a way of salvation for children who have died without Baptism. All the more urgent is the Church's call not to prevent little children coming to Christ through the gift of holy Baptism”.
Now, to answer the question this article asks... no, the Church has not changed the teaching on the necessity for the Sacrament of Baptism. The only way any such speculation would have the affect of "changing dogma" is if another definition was made, using the proper formula, which would be contrary to the initial dogma - and THAT has never happened.