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you can use this tool http://interconnectit.com/products/search-and-replace-for-wordpress-databases/ to replaces the urls. The advantage over SQL replace is that the tool know how to handle serialized info in the DB.
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Being easy to sync is problematic requirement with the way you are trying to do things. If you need that, then you should simply change your localhosts file to point olddomain.com to 127.0.0.1 and then you will not need to do any alterations to code or data. This is the right way to go especially if you have a dedicated testing machine.
