TB54 the message will comes back to it's original place (the one of its number) when the update will come?
From what I understand from the Pull Request that was merged into Flarum, it will be retroactive yes, because it changes the column used for sorting in the SQL requests, so it will affect all existing discussions as well.
I wasn't aware of this change until now, I was reviewing the Flarum code on master branch to see how sorting is done and noticed it was changed from what I remembered. There's also an issue that outlines some of the reasons for the change flarum/framework3281
Unfortunately Flarum doesn't have any good way of re-ordering posts or adding posts in between existing ones. As the issue points out, not ordering by post number causes issues with perma-linking. But re-numbering posts would cause perma-links to change as well so there's really no good solution available at the moment 😬
Maybe perma-links should be decoupled from discussion pagination at some point. Post numbers in the URL could be kept to linking to a specific place in the discussion (nth-post), while a different perma-link would contain the post ID and redirect to the correct post number dynamically when accessed. It's less elegant, but would probably be the best option to add flexibility to the post stream without needing to change how the infinite scrolling and pagination works.