This question already has an answer here:
nothing in hinduism in enforced strictly. large numbers of non-hindus have converted through "common law" and thats that. I remember a strict elderly Iyengar emit smoke from his ears because a non-veg eating Nayudu chap claimed to be a vaishnavite and sported the namam. I guess over generations such "Hindus" lost their quotes.
According to Wikipedia: "Ghar Wapsi (Hindi, meaning "Back to Home") is a series of religious conversion activities, facilitated by Indian Hindu organizations Vishva Hindu Parishad (VHP) and Rashtriya Swayamsevak Sangh (RSS), to facilitate conversion of non-Hindus to Hinduism"
Does this have a scriptural basis?
does it make a difference if it is a re-conversion - a hindu who converted to another religion and wants to come back?