After a sound caution about unity (not uniformity!) we encounter elements for which bishops’ conferences may offer norms.
54. For the celebration of the eucharist, the Roman Missal, “while allowing … for legitimate differences and adaptations according to the prescriptions of the Second Vatican Council,” must remain “a sign and instrument of unity” (apostolic constitution Missale Romanum 221) of the Roman rite in different languages. The General Instruction on the Roman Missal foresees that “in accordance with the constitution on the liturgy, each conference of bishops has the power to lay down norms for its own territory that are suited to the traditions and character of peoples, regions and different communities.” (old GIRM 6, GILM 111-118) The same also applies to
- the gestures and postures of the faithful, (old GIRM 22)
- the ways in which the altar and the book of the Gospels are venerated, (old GIRM 232)
- the texts of the opening chants, (old GIRM 26)
- the song at the preparation of the gifts (old GIRM 50)
- and the communion song, (old GIRM 56i)
- the rite of peace, (old GIRM 56b)
- conditions regulating communion with the chalice, (old GIRM 242)
- the materials for the construction of the altar and liturgical furniture, (old GIRM 263, 288)
- the material and form of sacred vessels, (old GIRM 290)
- liturgical vestments. (old GIRM 304, 305, 308)
Episcopal conferences can also determine the manner of distributing communion. (Cf. De Sacra Communione et de Cultu Mysterii Eucharistici Extra Missam, Praenotanda, 21)
Note the secondary level of music at Mass: the texts of the propers–this is something to be determined (or at least strongly influenced) at the national level.
As for the rest, vestments, materials, furniture, ways of veneration–probably less of interest to us, especially given the wide variety from parish to parish in most of that.