It is prohibited for a priest to change the words of Christ in the Gospel reading for any reason. The Code of Canon Law states "the liturgical books approved by the competent authority are to be faithfully observed in the celebration of the sacraments; therefore, no one on personal authority may add, remove, or change anything in them" (CIC 846 §1).
In Sacrosanctum Concilium, we read "therefore no other person, even if he be a priest, may add, remove, or change anything in the liturgy on his own authority" (22).
Other statements on the liturgy:
- In the readings, the table of God’s word is prepared for the faithful, and the riches of the Bible are opened to them. Hence, it is preferable to maintain the arrangement of the biblical readings, by which light is shed on the unity of both Testaments and of salvation history. Moreover, it is unlawful to substitute other, non-biblical texts for the readings and responsorial Psalm, which contain the word of God. (GIRM 57)
- The norms laid down in the Lectionary concerning the number of readings, and the directives given for special occasions are to be observed. It would be a serious abuse to replace the Word of God with the word of man, no matter who the author may be. (Inaestimabile Donum: Instruction Concerning Worship of the Eucharistic Mystery 1)
For help on how to address a liturgical abuse, I recommend Jimmy Akin’s book, Mass Confusion. You also might want to read Lou Bruno’s article "How to Address a Liturgical Abuse," available online at www.adoremus.org.