You may need to merge blog post content if you want to change domains and retain search engine rankings or you could lose a large chunk of your targeted traffic.
In my opinion, one of the best ways to consolidate your content onto one domain would be to use the WordPress import tool and import your posts, pages, categories, tags and attachments to your old domain.
Changing URL's When Merging Domains
You could then create a full backup and restore all your consolidated content onto your new domain using a backup & restoration plugin so all your URL's including image attachment URL's will be changed to your new domain.
Simply importing your content using the WordPress import tool, to your new domain will not change your attachment URL's for your images which would then remain hosted on your old domain.
Even if you used a tool like velvet blues plugin to change your URL's to your new domain, your images would still be hosted on the old domain.
One solution to fix this problem would be to combine all your images into one media directory on your new domain server and then change the URL's using either of these 3 plugins discussed in this post.
There's also a search and replace plugin which you could use to change any URL's that need changing.
Here's the backup & restoration process
- Import all content from one domain to the other using the WordPress export/import tool
- Create a full backup of the consolidated content using a backup plugin
- Migrate and restore all your backed up content to another domain using the backup plugin
Moving to a New Domain
The reason i wrote this post is because i believe the best method when changing domains is to publish content to your new domain for 3-6 months before making the move. You would then need to combine all that content onto one domain using the method i have described previously.
Search Engine Results After Merging Domains
Once you've got your new domain producing page rank and domain authority, your content should rank better in the search engine results which wouldn't be the case if you simply moved your old content to a brand new domain without any content ranked on its own.
This post is based on my own experience when moving content after changing domains and monitoring Google Webmaster Tools & SEOMoz data for keywords, search queries, links, page rank and domain authority.
I've read many articles on Matt Cutts blog, SEOMoz and other well known Seo experts blogs which don't show any real life examples of what actually happens when your move content to a new domain causing a change in URL's.
This is the best method to use when Changing domain names and moving WordPress to a new site address.