Hi AnnaG. I am not the best person to answer your inquiry, although it appears no one else is.
Traditionally, kneeling was banned on Sundays, since some of the earliest days of the church (~325 AD). The reason is that kneeling is a penitential posture, and on Sundays we celebrate the resurrection and victory over sin and death. In early Christianity, kneeling on Sundays was seen as denying Christ's resurrection.
In Western Christianity (Roman Catholics), practices diverged over time (e.g., kneeling on Sundays and some other things). There's a bit of discussion here:
https://www.byzcath.org/forums/ubbt...ly-church-canons-and-kneeling-on-sundaysYour parish's former practice was what's known as latinization, or replacing our authentic Eastern traditions with Western/Roman traditions. Especially since the Second Vatican Council (1960s), there has been a drive to remove latinizations and return to our traditions. Part of this standing. Some related discussion is here:
https://www.byzcath.org/forums/ubbthreads.php/topics/73680/a-question-about-latinizationsThe different hymnal tunes is probably just a liturgical choice. For most parts of the Liturgy, there are options for which tune to use.
As for why your parish never used to use the title "Theotokos," I have no clue.
Let me know if you have more questions (and maybe someone else can help answer as well). I hope this helps
