It seems straightforward, concerning customs - such as not eating rice on Passover, which is current in several places - that they are followed because one's forefathers followed them, but one's students are certainly not obliged to follow them. If so, this is the rule for all halakhot performed by teachers who are following their forefathers' customs. It would therefore seem that a Ba'al Teshuva [penitent, newly religious] who has been returned to the fold by rabbis or heads of yeshivot, whose forefathers' customs are not identical to his forefathers' customs, should follow his own forefathers' custom - despite his having studied with them. In the case that his father is not observant of the Torah and its commandments, he should act as did his ancestors, on the basis of 'not abandoning your mother's teaching', and because these are the ways our forefathers took upon themselves and upon their children and their children's children.