When  you rename a blog, the most that you can do, to keep the old URL useful, is to setup a stub post , with a clickable link to the new URL. Yo!  The blog is now at xxxxxxx.blogspot.com!! Blogger forbids gateway blogs, and similar blog to blog redirections .   When you rename a post, you can setup a custom redirect  - and automatically redirect your readers to the post, under its new URL.  You should take advantage of this option, if you change a post URL.  
What Blogger won't tell you
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