I had a long conversation with an Orthodox Rabbi on this subject concerning the Mormons who converted dead Jews to the Mormon belief. The Rabbi explained that the Jewish law (Halacha) states simply, "Once a Jew, always a Jew. A Jew is G-d's Chosen people." I tried to make it difficult, so I asked, "What if the Jew converts?"
The Rabbi emphasized, "It will not help him/her. G-d Has Chosen him/her and he or she can not backtrack on G-d's Decision. This is the law (Halacha)." To clinch this argument. He pointed out to me, "So even if he/she converts, they can be buried in a Jewish cemetery in full Jewish ceremony when they die. All the best,
Shana Tova and may we all enjoy this coming new Year in very good health.
Aizic Sechter from the Lone Magen David State of Israel