Is it allowed to deviate from the Catholic Liturgical Calendar during a pilgrimage? Later this year I am helping to lead a Marian pilgrimage. The days we are away are all non-Marian feasts or obligatory memorias. (Following the general Catholic Liturgical  Calendar.)

Is it permissible according to Catholic rules to celebrate votive Marian masses during the pilgrimage in place of the masses of the day?
Under certain conditions, the clergy may employ a votive mass on days where it is permitted in honor of the Blessed Virgin Mary, especially on Saturdays. Traditionally, Saturdays are dedicated to Mary.

What is a votive mass? 


  Votive Mass
  
  A Mass offered in honor of some mystery of the faith, or the Blessed Virgin, or of a saint or all the saints, but not in the liturgical calendar for that day. Votive Masses, with some exceptions, may be offered on any ordinary ferial day in the year, outside of Lent and Advent, and on other days that do not require the Mass of the day to be said. In general, votive Masses may be taken from among those listed as votive in the Roman Missal or from any other Mass of the year.


The General Instruction of the Roman Missal, No. 376, has this a say about votive masses:


  "On obligatory memorials, on the weekdays of Advent up to and including December 16, of the Christmas Season from January 2, and of the Easter Season after the Octave of Easter, Masses for Various Needs, Masses for Various Circumstances, and Votive Masses are as such forbidden. If, however, required by some real need or pastoral advantage, according to the judgment of the rector (pastor) of the church or the priest celebrant himself, a Mass corresponding to such a need or advantage may be used in a celebration with a congregation."


But that is not all. The Vatican, under Pope John Paul II, published a Collection of 46 Marian Masses in 1986. Some of these masses are permitted to be celebrated in Advent, Easter and Lent.


  The Collection of Masses of the Blessed Virgin Mary, published by the Congregation of Divine Worship in 1986, is a set of forty-six Masses intended for use at Marian shrines and for communities who wish to celebrate the Memorial of the Blessed Virgin on Saturday. Originally published in two volumes, a Missal (Sacramentary) and a Lectionary, its status as an official liturgical book confers an authority both on the individual Masses as well as the principles contained in the General Introduction.
  
  The forty-six Masses are arranged according to the divisions of the liturgical year: Advent (three), Christmas (six), Lent (five), Easter (four), and Ordinary Time (twenty-eight). The Advent season celebrates "the two comings of the Lord: the first in lowliness when ... the Lord took flesh of the Virgin Mary ... and the second in glory, when ... the Lord will come to judge the living and dead and to lead the just ... where Mary has preceded them in glory." During Lent, Mary is "the model of the disciple who faithfully listens to the word of God and follows the footsteps of Christ to Calvary ...." - Collection of Masses of the Blessed Virgin Mary.