The Vrātya-stōma was the typical ceremony performed for admitting foreigners into the Sanatana society during the pre-Islamic period. It is still valid for foreigners who formally want to become Hindus.
A brief introduction to the Devala-Smriti, a very ancient Dharmasastra treatise. In the 10th century, a chapter titled Mlēccita-Śud'dhih was added to it, dealing with the reconversion of Hindus back to their original Dharma
