Is repeating the lyrics of a song that include standing by a church and feigning prayer inside it considered a form of apostasy that expels one from the religion?

All praise is due to Allah, who guided you and accepted your repentance. For a person to say about themselves that they have a church and pray in it is an act of disbelief (kufr), Allah forbid, because it implies, "He is a Christian." And whoever says that is judged to be a disbeliever. Sheikh Ibn Uthaymeen mentioned that whoever utters a statement that takes him out of Islam, such as saying, "He is a Jew" or "He is a Christian," is a disbeliever and an apostate. Since you have repented from this sin, praise Allah and continue on the path of righteousness.