NOTE: To copy 1 attribute to 1 or more categories where you already have Option Names and want to add 1 more option value you can do this in the Option Value Manager ...

Say you want to add the Color Pink to all Products with the Color Red in categories_id 45 ...

Look in the Option Values Manager and you will see:
Copy to ALL Products where Option Name and Value ...
Select an Option Name and Value that currently exists on a product or products that you then want to copy another Option Name and Value to for all products with this existing Option Name and Value
Pick from the Option Name From: COLOR and Option Value From: RED
Pick from the Option Name To: COLOR and Option Value To: Pink
Pick categories_id 45