About visors in the NHL, the talking heads are being a little lazy and imprecise by saying visors will be 'grandfathered'. That's not accurate or descriptive, they're using a hockey term that fans know, but by overusing it they're fuzzing up the definition.
What is accurate to say is that visors might become mandatory next season, with an out clause for current players who don't want to wear one grandfathered in. So visors aren't grandfathered, they're being made mandatory.
A grandfather clause is a provision in which an old rule continues to apply to some existing situations, while a new rule will apply to all future cases.