"change his religion means he has left all his rights in his family & property." - wrong.
no law is there that, change of religion will deprive one, from his property or caste benifit. on the contray property is one's constitutional right. caste benifit given to one's caste bassis, not religion basis. religion is changeable not caste. i have seen several cases where caste benifit remains intact after change of religion. the party officially inform about his change of religion to his office, central govt - undertaking.
perhaps one supreme court rulling is also there in this effect. but i do not have it.