For more details see the Duplicate Categories extension page.
Create the exact copy of the existing categories in a number of clicks. Dramatically save time on duplicating categories in multi-store configurations.
The module allows you to duplicate categories using the default Magento interface. Navigate to Catalog → Manage Categories. Then, select on of the existing categories and the Duplicate category button will appear.
Next, at the duplication page you can specify some details:
Select Parent Category — tick the parent category that will be duplicated;
Copy Product Relations — enable this option to copy product relations;
Include Subcategories — enable this option to duplicate subcategories together with the main category.
Then, navigate to the Search and Replace section.
You can make replacements in the following fields of the duplicate category:
Words from the Search For fields will be replaced with content from the Replace With field.
Hit the Duplicate button to create the copy of the category.