Condless

WooCommerce plugin that sets default attribute for variable products automatically if only 1 option is in-stock.
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Variable product of T-shirt with color attribute (White/Blue/Black) and size attribute (S/M/XL): 
If only Black T-shirts are in-stock: default color (Black), default size (none). 
If only Small T-shirts are in-stock: default color (none), default size (Small). 
If only White and XL T-shirts are in-stock: default color (White), default size (XL).
<h4>How It Works</h4>
<ol>
<li>Before product variations is displayed to the customer, the plugin will check each attribute, and if there is only 1 in-stock option it will be set as the default.</li>
</ol>
<h4>Features</h4>
<ul>
<li>Stock: Set option as default when it’s the only 1 in-stock.</li>
<li>Per Attribute: Set specific option as default in all products with that attribute (from the Edit Attribute screen)</li>
<li>Top: Set as default the first option of each attribute.</li>
<li>Out of stock: Disable out of stock variations.</li>
<li>Add to Cart button: In archive pages display for variable products the attribute name instead of: “Select options”.</li>
<li>Select options: In single product pages remove the select options text if default attribute is set.</li>
</ul>

Default Attributes for WooCommerce

WooCommerce plugin that sets default attribute for variable products automatically if only 1 option is in-stock.

ALEX ARCIGA

This plugin adds a “Duplicate Attribute” page under Products in the WordPress admin, allowing you to:
<ul>
<li>Duplicate WooCommerce global product attributes</li>
<li>Copy all attribute settings (name, slug, type, order by, visibility)</li>
<li>Copy all attribute terms in the same order</li>
<li>Copy all term meta (e.g. color preview codes, custom fields)</li>
<li>Preserve parent/child hierarchy for terms</li>
</ul>
Perfect if you need to quickly replicate existing attribute taxonomies for new products or stores.
<h3>License</h3>
This plugin is licensed under the GPL v2 or later. 
You are free to use, modify, and distribute it.

Duplicate Attribute

Duplicate WooCommerce global product attributes including all terms, term order, and term meta (like color previews).

Default Attributes for WooCommerce vs Duplicate Attribute