When I change a slug from
post-b, will WordPress create a redirect from
/post-b, like HTTP 301 or something similar? If not, is there a plugin for that?
I just went and tested this (WP 3.3.1), the wordpress core will automatically do a redirect if you change the post slug, even if you change the slug from
post-b and then to
post-a will return a 301 to
post-c. That said, the redirection plugin that Mike Jolley recommended is an outstanding plugin and a great way to monitor for 404 errors and such.
This plugin can be used to monitor URL changes like that and set up redirection automatically: