quokka.au changed from Lemmy to PieFed and it was ok once the remote servers refreshed their public key caches, about a day.

Mastodon to GTS could turn out different but yeah.

while I don't know the answer to the question, I am very certain that

or would whole fediverse crash

is not it; if that could make the whole fediverse crash, someone could do it maliciously. At most it will cause problems delivering your messages or delivering messages to you.

I'm not a technical person, so i don't really know, but from a blog i read about switching from lemmy to piefed, i guess there should be some problems :

I also changed the URL from jemmy.jeena.net to piefed.jeena.net because I don't want the other instances to be confused when suddenly a different software with different contents is available under the same domain. But I'm thinking to start up Lemmy and unsubscribe from all communities and to delete the one community I have on my Lemmy instance which has only very few subscribers.

That at least would be a somewhat clean way to dispose of this lemmy instance. Oh and I should return a 410 Gone to indicate that it's permanently gone.

I changed Ruud.social from akkoma to sharkey. It still works.

I changed kbin.earth from kbin to Mbin, and it's been working great. It definitely helps that Mbin is a fork of kbin.

It definitely depends on the software, for example in matrix you can easily cause federation issues in some cases. this won't blow up the fediverse, but it could impact the user experience if they rely on or interact with that instance.