The only achievement that was ever changed was complete a GM to replace Prestige Leviathan -- which is a -blam!- steal. The base game has always had NFs available to base game players. But I believe studios have to pay MS and Sony to certify achievements and Bungie figured they would just create their own in-game achievements and forgo the money and process altogether.

This was it "Destiny 2 players could no longer access the Prestige raid or Nightfall activities, and therefore no longer complete the base game's achievement/trophy lists or acquire the Legend of Acrius exotic shotgun." "To make matters worse, our team overlooked the fact that both of these mistakes disabled Trophies and Achievements for Destiny 2. This was an unacceptable lapse on our part, and we can understand the frustration it has created." Today's planned update to the game will address all of the https://www.eurogamer.net/bungie-admits-it-made-mistakes-locking-off-in-game-content-behind-dlc I forget the finer details but it was a big thing and one of the stores (Xbox or PSN) tweeted bungie directly reminding them that all base game achievements needed to be completable within the base game or they'd be removed from the online store. They made the same mistake a year or so later and had to make it where there where 2 nightfalls available weekly, one base & one dlc, I think that was achievement related too.