I think I know what you are referring to. If I understand correctly, then this plugin will do the trick:
http://wordpress.org/plugins/quick-pagepost-redirect-plugin/
Say the page on your menu goes to mydomain.com/samplepost but you want it to actually go to mydomain.com/newsamplepost then this plugin will allow you to create a permanent quick redirect so that anyone clicking on the menu item or going to mydomain.com/samplepost will automatically see mydomain.com/newsamplepost
Hope this helps!
Mike