Q. 1. Can the priest change when the Sign of Peace if given during the Mass? For example, can we have it when the Holy Mass starts?
A. 1. The Sign of Peace follows the "Lord's Prayer" during the "Communion Rite." No one has the authority to change, add, or delete from the Liturgy of the Holy Mass. Such is regulated by the Vatican.
Canon Law # 838 §2. "It is for the Apostolic See to order the sacred liturgy of the universal Church, publish liturgical books and review their translations in vernacular languages, and exercise vigilance that liturgical regulations are observed faithfully everywhere."