Q: When I preside at Mass during the Christmas Octave, how do I add the special Communicantes to Eucharistic Prayers II and III?
A: You don’t. They belong only to Eucharistic Prayer I. In addition to the preface, they connect the prayer to the season. The Roman Canon has a long tradition of including these special acknowledgments on certain days throughout the year. But the other prayers didn’t receive them.
Some other language groups do have inserts in Prayers II and III. The new Italian missal is one example. But when the US got our English translation, we were not allowed to add anything that was not in the Latin original. By the time the Italian translation came out, the rules had changed.
I use Prayer I throughout the octave just so I can use that extra line about Christmas.