grandfather sb/sth into sth
also grandfather sb/sth in— phrasal verb with grandfather uk/ˈɡrænfɑːðər/usverb US LAW
to allow someone to continue to do or to have something that a new law or rule makes illegal:
Most existing companies will be grandfathered into the old system for up to five years.
Many old bridges will suddenly be out of date but will be grandfathered in.