grandfather in
To exempt certain people or businesses from new limitations or restrictions, thus allowing them to continue doing or benefiting from something as they did before. This can be done through the use of a "grandfather clause." A noun or pronoun can be used between "grandfather" and "in." If they change the pension plan, they better grandfather us in!
grandfather someone or something in
to protect someone or a right through the use of a grandfather clause. My payments were grandfathered in years ago.