Selected Responsa 133
Hayim Shor(Torat Hayim#17) and Samuel Ungar(Mekadshei Hashem, p. 214; R. Kirschner, Anthology of Holocaust Responsa, pp. 97 ff). It is clear from these statements that these rabbis took a hard line with a baptismal certificate which seemed like an outright denial of Judaism , but were willing to go along with anything less.
Other authorities during the Holocaust , however, decided differently even on the matter of baptismal certificates. They realized that(a) the Nazis were not interested in converting anyone to Christianity ;(b) they made such conversions punishable by death;(c) they severely punished Christian clergy involved in such an act of mercy. For these reasons the number of Batei Din in Poland , Czechoslovakia and Hungary , as well as Lithuania , permitted such baptismal certificates to be held by Jews , and treated these Jews as any other member of the Jewish community despite protests within the community. Any other action seemed to play directly in the hands of the Nazis , and the rabbis certainly did not wish to do that(H.J. Zimmels, The Echo of the Nazi Holocaust in Rabbinic Literature, pp. 77 ff). Similarly, it was permitted for individuals to declare themselves Karaites as they were not considered Jews under various Nazi rulings(Ibid. 88 ff.).
The main line of thought among both Medieval and modern commentators prohibits an outright denial of Judaism , but permits an ambiguous statement which can be interpreted as a denial by the persecutor. It also permits a disguise which would Not cause any questions to be asked.
The Medieval authorities also distinguished types of persecution. If the persecutor wished to force Jews to accept another religion, then it was the duty of the Jew to resist even if it meant death. If, however, it was the intent of the persecutor merely to persecute the Jew and threaten him with death without any interest in turning him into an idol worshipper, then he could