When someone changed his or her faith to Russian Orthodoxy, it was recorded in birth records (which are actually “christening records“). Often people changed their name as well.
An example from church in Konotop town:
Boy Shmerka Avramov Kerlin christened as Ioann, Ivanovich Buryachenko in his godfather’s name. Change in middle and last name (and the age of the boy) suggests that he was also adopted by Ivan Kirillov Buryachenko.
Шмерка Аврамов Керлин
Иван Иванович Буряченко
Иван Кириллов Буряченко
Смотрите также: “Jewish birth records in Russian Orthodox church records” и “About Russian Orthodox birth records”.