The changing of official lore means next to nothing for any campaign. If there is a lore change that a gaming group doesn't like, they already have their established lore that they can and should stick with. Your campaign history is what you want it to be. It does not affect any table outside of the unreasonable expectation that lore never changes.
The old books with older lore are still available if desired, like on DM's Guild if you don't already have your own copies.
For example, my D&D campaign setting does not have Slaad. Like at all. An epic PC was able to erase them out of existence (which was pretty awesome). Changes in slaad lore do not mean they appear in my campaign.
Another example, "Gruumsh" isn't a thing in my world. My world has 2 types of orcs, even before the 2024 rules changed them. One are the pig-faced monstrous orcs, and the other are the "hotter" orcs, that the 2024 book better represents. They each have their own origin (transplanar in nature), but use the same stats. They differ in culture and society.
Both yes and no.
I mean, it's a hearty yes because tables make their own lore... or, at least, many do. There's a lot of tables that
only use official lore and/or
only run modules or whatever, in large part because they don't have the time, energy, or imagination to make their own, or somehow think that anything official is somehow superior to their own measly attempts at worldbuilding.
But it's also a bit of a no because, as I mentioned, every subsequent book will reflect the official lore. That makes it harder to disentangle the lore from the lore. As an example, I had to do a lot of rewriting to make
Curse of Strahd fit with my preferred interpretation of Barovia because it added a bunch of really weird things I wasn't fond of (a walled town that ate mostly wolf meat, a town that had weekly you-will-have-fun-citizen festivals, the stupid, jokey epitaphs in the crypt) and removed things I liked (the Red Vargo Trading company, the occult shops of Vallaki, the entire town of Immol, everything I liked about Inajira). So, to keep the to the older lore, I had to do a
lot of work, and in the end it felt like a mess. All in all, I would have been better off making my own adventure, but I've given up my dreams of having epic campaigns and realized my strengths lay in a more episodic style of play.
So this goes beyond replacing any slaadi in an adventure with some other monster. I like quite a bit of the new Ravenloft lore from VRGtR, and if I were to start up a new Ravenloft game I'd use it primarily. But if WotC were to put out a new sourcebook or adventure, it would be completely useless to someone who
only wants the older lore.