- First of all, you may lose any of your loyal visitors who frequently visit your blog, if they are not informed about this change.
- Secondly you will lose your Alexa ranking, which solely depends on your blog's url.
- Thirdly if you have any pages bookmarked in social bookmarking websites, then those links will now be considered as invalid links.
- And lastly if you have been linked by any other blogs with your present blog's address, then you will even lose the link juice you were previously getting.
Log in to Blogger,
Now go to "Settings" -> "Publishing" tab.
Alternatively, you can follow this method (In case you do not have too many posts in your present blog):
Create a new blog, with the desired blog-address.
Export your present blog (From Settings -> Basic tab).
And now import your present blog to the new blog.
By this method, both your blogs (new and old) will be live and you can place some banners at your present blog, for your regular readers, telling them about your new blog, making sure that you do not leave anyone behind.
NOTE: If you are planning to shift to a custom domain, then I would suggest you to do it without delay despite of the disadvantages described above, because you not only get a professional domain, but you can also redirect your present web-traffic to the new domain easily. Also remember that with increasing web traffic and popularity of blogs, global TLDs are now really very difficult to register (as most of the web-domains are already registered), so if you are serious about blogging then register a domain as soon as possible (it hardly costs you $8/9 per domain per year).