The expression "grandfathered in" or similar expressions like "grandfather clause" aren't always immediately clear to people for whom English is a second language.
But I'm hard pressed to come up with a synonym that captures the same meaning while also being easy to comprehend, and preferably more inclusive (the history of grandfather clauses isn't that great, and the notion that someone's grandfather would need special exemption seems less than ideal).
Is there a synonym (either a single word or a phrase would be fine) to express the idea of something being allowed or special-cased for existing instances but for which future instances are prohibited or discouraged?