Can a parish change the Liturgy of the Word set for a weekday or weekend Mass?

Can a parish change the readings, psalms and gospel set for Holy Mass (i.e. either a specific weekday or weekend - to include Sunday) to something different that what is published elsewhere (e.g. USCCB or Magnificat)? I thought that the Vatican set the schedule, is there an “official” source for the readings, psalms and gospel that all dioceses need to follow? If they cannot change the Liturgy of the Word, but do change it, should we report it to the parish pastor or the diocese?

On Sundays and solemnities the readings are set by the Church. On weekdays the readings are also set by the Church but there is a bit more flexibility:

General Instruction of the Roman Missal

  1. …For memorials of Saints, unless strictly proper readings are given, the readings assigned for the weekday are customarily used. In certain cases, readings are provided that highlight some particular aspect of the spiritual life or activity of the Saint. The use of such readings is not to be insisted upon, unless a pastoral reason suggests it.
  1. …If, however, the continuous reading during the week is interrupted by the occurrence of some solemnity or feast, or some particular celebration, then the priest, taking into consideration the entire week’s scheme of readings, is allowed either to combine parts omitted with other readings or to decide which readings are to be preferred over others.

In Masses with special groups, the priest is allowed to choose texts more suited to the particular celebration, provided they are taken from the texts of an approved lectionary.

As for the Psalm, even on Sundays there are options:

GIRM 61. In the dioceses of the United States of America, the following may also be sung in place of the Psalm assigned in the Lectionary for Mass: either the proper or seasonal antiphon and Psalm from the Lectionary, as found either in the Roman Gradual or Simple Gradual or in another musical setting; or an antiphon and Psalm from another collection of the psalms and antiphons, including psalms arranged in metrical form, providing that they have been approved by the United States Conference of Catholic Bishops or the diocesan Bishop. Songs or hymns may not be used in place of the responsorial Psalm.

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