How to redirect just one or two blog posts correctly?

First, make sure that Rewrites are enabled for your server, then add this to your .htaccess file in WordPress’s root directory…

RewriteRule your-old-page-permalink/ http://www.yoursite.com/your/new/permalink/ [R=301,L]

This is a greedy match, so your-old-page-permalink/ just needs to correspond to the old post’s SLUG (that’s the editable part of the permalink on your post edit screen).

So, go to your admin, grab the old permalink slug, add a rewrite rule to your .htaccess, and then change the permalink in WordPress to whatever you want (making sure the RewriteRule matches the new url as well). Do this for each post whose permalink you want to change.

One more thing…

Be sure to put this rule at the top of your .htaccess file… or at least BEFORE WordPress’s auto-generated rewrite rules. The L means “Last” and will stop execution… and since WordPress has L rules itself, if this is put after, it will never trigger.

Also, if the redirects don’t seem to be working as-is, add this above them (which will activate rewrites if they aren’t already)…

<IfModule mod_rewrite.c>
RewriteEngine On
</IfModule>