Sherice Jacob at Search Engine Journal has written a pretty nifty article on how to change your domain without compromising your rank in the SERPs. It has in-depth information on how to update both your mod_rewrite components and .htaccess file so you actually have a bit of flexibility in the event you're selling a piece of your site, you're widening the focus of your niche, or a more relevant domain happens to free up!
You’ve had your domain for a long time and it has served you well. Today, though, you’re looking to expand your online business and the old domain just won’t do the trick. You need something new, fresh and exciting and perhaps you’ve already registered the ideal name.
There’s just one problem.
Your old site has earned a good search engine ranking for your best keywords. You’ve got tons of “link juice” to both give and receive - and you don’t want to lose that.
Keep in mind, we’re not just moving files or folders here - but moving an entire site to a new domain name without it affecting your ranking. To do this, you’ll need two tools - .htaccess and mod_rewrite.
How to Change Your Domain While Keeping Your Search Engine Ranking