I’ve noticed that when inserting links to other posts/pages using the visual/html editor, WordPress uses the url-structure chosen in the permalink settings.
Is it possible to use the standard permalink structure (yourdomain.com/?p=123) in the editor’s link-dialog?
This way, I would be able to change the slug of the post or page I’m linking to, while still maintaining an active link.
It would make more sense to use a plugin like Redirection to automatically add htaccess redirects to redirect crawlers to the new address if you decide to change the permalink for a post down the line instead of exposing the ugly permalink to the public (and risk its being shared and indexed). Redirection has a setting that will add new redirects whenever you change a permalink automatically, so you don’t have to do anything when you change links.