I remember reading some interesting stuff years ago about the Japanese persecution of Christianity. The faith was driven underground, its practitioners had to outwardly adapt Shintoism to survive while passing their faith down in secret, by word-of-mouth, and often with no priests or written Scripture available. By the time the prohibition was lifted and underground Christians were able to practice their faith openly, it had evolved into a hybrid between the two, one that still exists today.
yes and no from my experience - it wasn’t much different from the survival in the early years among the romans.