@gnomon Replacing URLs isn't that hard, whether there's hundreds of them or thousands - a properly written script doesn't care.
I mentioned lore (and the LWN mailing-list archive) in particular because they are based on public-inbox. That is a great piece of software, but it has some interesting design decisions. Behind public-inbox is a Git repository with a single file called "m". Each message added to the archive goes in as a patch to "m". A mailing-list archive is a long series of Git commits to that one file.
What this means is that changing a message in the archive comes down to a rebase operation. Lots of fun in an archive with millions of messages (and thus millions of commits to rebase) in it. It's doable, but it's not fast or easy. It's not what public-inbox was designed to do. Archived emails aren't meant to change.
Changing URLs in an email will also mess with things like DKIM validation, of course.
This is why I think it's unlikely that the linux-kernel archive (or the LWN archive) will be patched; it's a massive job. But perhaps
@monsieuricon has a different view of things...?