Pope Francis made some recent comments in a letter, which are being summarized in headlines like, "Pope Francis tells atheists to abide by their own consciences."
Does the full context of the Pope's remarks represent a change in doctrine?
A change in doctrine, if it is possible at all, can only be expressed with a definitive statement ex cathedra. The Pope wrote in his letter
Le accolga come la risposta tentativa e provvisoria,
Please accept this as a tentative and provisional response
so no, it does not express any change in doctrine.
In the English translation, the Holy Father writes
Each of us is called to accept the view and the choice of love made by Jesus, become a part of his way of being, thinking and acting.
That is a definitive statement of what God expects of mankind.
He goes on,
First of all, you ask if the God of the Christians forgives those who do not believe and do not seek faith. Given that — and this is fundamental — God's mercy has no limits if he who asks for mercy does so in contrition and with a sincere heart, the issue for those who do not believe in God is in obeying their own conscience. In fact, listening and obeying it, means deciding about what is perceived to be good or to be evil. The goodness or the wickedness of our behavior depends on this decision.
This is saying much the same thing as Benedict XVI did when he spoke about the use of condoms in combatting AIDS. Consideration of one's actions and the reasons for them is the first step on the road to faith.
In explaining that God's mercy has no limits, Pope Francis writes "if he who asks for mercy does so in contrition and with a sincere heart". That presupposes that the person asking for mercy is asking of a God he believes in [or who is he addressing?] and with sorrow for not having believed in the past. The Pope has not contradicted the tenet that belief in God is necessary; far from it. What he has done, though, in directing people to obey their conscience — their God-given sense of good and evil — is to point them in the direction of God.
Both Popes are encouraging that first step in searching out the truth.
[Truth is not] variable and subjective ... it is given to us only as a way and a life. Was it not Jesus himself who said: "I am the way, the truth, the life"? In other words, the truth is one with love, it requires humbleness and the willingness to be sought, listened to and expressed.
Seek the truth; find it and repent; and you will enter heaven. This is consistent with the teaching of the Church.
I will quote the Council of Florence and let you draw your own conclusions.
Pope Eugene IV, Council of Florence, “Cantate Domino,” 1441,
“The Holy Roman Church firmly believes, professes and preaches that all those who are outside the Catholic Church, not only pagans but also Jews or heretics and schismatics, cannot share in eternal life and will go into the everlasting fire which was prepared for the devil and his angels, unless they are joined to the Church before the end of their lives; that the unity of this ecclesiastical body is of such importance that only for those who abide in it do the Church’s sacraments contribute to salvation and do fasts, alms giving and other works of piety and practices of the Christian militia produce eternal rewards; and that nobody can be saved, no matter how much he has given away in alms and even if he has shed blood in the name of Christ, unless he has persevered in the bosom and unity of the Catholic Church.”
Decrees of the Ecumenical Councils, Vol. 1, p. 578; Denzinger 714.