No, the Catholic understanding of justification not occurring by grace alone has not changed. The 1999 Joint Declaration on the Doctrine of Justification has not created any new doctrine, but restates Catholic doctrine on this point.
The Canons of the Sixth Session of the Council of Trent include, among others, the following statements:
CANON I. If any one saith, that man may be justified before God by his own works, whether done through the teaching of human nature, or that of the law, without the grace of God through Jesus Christ; let him be anathema. [This, note, is the very first statement made.]
CANON XXIV. If any one saith, that the justice received is not preserved and also increased before God through good works; but that the said works are merely the fruits and signs of Justification obtained, but not a cause of the increase thereof; let him be anathema.
CANON XXXII. If any one saith, that the good works of one that is justified are in such manner the gifts of God, as that they are not also the good merits of him that is justified; or, that the said justified, by the good works which he performs through the grace of God and the merit of Jesus Christ, whose living member he is, does not truly merit increase of grace, eternal life, and the attainment of that eternal life,—if so be, however, that he depart in grace,—and also an increase of glory; let him be anathema.
That is, the Council of Trent wanted to underscore that the teaching of the Church regarding justification includes the following points:
- Good works alone, without the grace of God, are not sufficient to justify anyone before God.
- However, good works are not merely "the fruits and signs" of justification, but activity which can, and must, be done by humans to merit further graces and ultimately salvation.
- Furthermore, these good works, though inspired by the grace of God, are not solely attributable to God, but to the doer of good works as well; and these good works will ultimately (all other things being equal) merit for the believer "the reward of eternal life" in Christ Jesus.
All these things are still taught by the Church. The Church still believes that good works do not alone justify anyone before God; this is the work of the Spirit:
Our justification comes from the grace of God. Grace is favor, the free and undeserved help that God gives us to respond to his call to become children of God, adoptive sons, partakers of the divine nature and of eternal life.
(Catechism of the Catholic Church, paragraph 1996)
And that good works are not just "fruits of justification" (though they are at least that), but work necessary for humans to participate in and merit salvation:
Moved by the Holy Spirit and by charity, we can then merit for ourselves and for others the graces needed for our sanctification, for the increase of grace and charity, and for the attainment of eternal life. Even temporal goods like health and friendship can be merited in accordance with God’s wisdom. These graces and goods are the object of Christian prayer. Prayer attends to the grace we need for meritorious actions.
(Catechism, paragraph 2010; emphasis added)
And, finally, that these good works we do are referable not only to God but more directly to us:
Merit is to be ascribed in the first place to the grace of God, and secondly to man’s collaboration.
(Catechism, paragraph 2025)
The Joint Declaration arrived at between Catholic and Lutheran theologians in 1999 extends to some very basic truths which both Catholics and Lutherans find acceptable; for example:
"All persons depend completely on the saving grace of God for their salvation." (paragraph 19)
"Good works - a Christian life lived in faith, hope and love - follow justification and are its fruits. When the justified live in Christ and act in the grace they receive, they bring forth, in biblical terms, good fruit." (paragraph 37)
None of these statements (nor the others stated in the Joint Declaration) conflicts with current or past doctrinal statements of the Catholic Church.