But if you are using Blogger, then you have got an option to bring back your older posts to the hompage whenever you want.
This is especially useful in seasonal events, when a post written in the past must be present on the homepage. But publishing a new post with the same content will cause content-duplication problems, so you can simply edit your previous post to change the publishing date and bring it back to the top.
So to do this, open the post-editor and click on Post Options link present in the bottom of the page. Now Set date and time to present or any future date.
Finally save the post and your work is done (You can of course undo the changes, to send the post back to its original place).
This technique is SEO friendly too, as you are not going to change the permalink of your post. In Blogger, when you publish a new post it gets a unique url in this format (http://YOURBLOG.BogSpot.com/YEAR/MONTH/Title_Of_The_Post.html)
which should and will remain the same, even after doing this hack.