"Category names must be unique among the child categories of a parent"

[Darius1968]

Right now, I have a tree - of IMatch categories - like this: 

--Clothing
-----Belt
-----Formal
-------Dress
------Footwear
-------Boots
-------Shoes
---------Loafers
-----Pants
-------Blue Jeans
-----Shirt

--Clothes
-----Apron
-----Formal
-------Suit
-----Footwear
-------Shoes
---------Loafers
---------Sandals

But I want to have (as easily as possible, and without a lot of labor): 

--Clothing
-----Apron
-----Belt
-----Formal
-------Dress
-------Suit
------Footwear
-------Boots
-------Shoes
---------Loafers
---------Sandals
-----Pants
-------Blue Jeans
-----Shirt

Now, I can't just rename "Clothes" to "Clothing".  Because IMatch flags this as:
Duplicate Category Names:  Category names must be unique among the child categories of a parent.

I could copy all child categories of the "Clothes" category, and then paste under the "Clothing" category.  But this has a side effect:  I am pasting child categories that (sometimes) have the same names as the categories already residing under "Clothing". 
So, it will work.  But what will happen is that I will get for example...

--Clothing
-----Formal
-------Dress
-----Formal 1
-------Suit

... instead of the two formal categories being merged as one.  Like this: 

--Clothing
-----Formal
-------Dress
-------Suti

So, how can I fix this without having to do a lot of tedious copy-and-pasting? 

[Mario]

Now, I can't just rename "Clothes" to "Clothing".  Because IMatch flags this as:
Duplicate Category Names:  Category names must be unique among the child categories of a parent.

This is correct.

There is no "shortcut" or magick trick. I think it will take about as long to drag the non-duplicate categories from Clothes to Clothing and then cut & paste the images (or drag) the images from the other categories than it takes to write this post. I do that so often, I don't even think about it. It takes mabye 2 seconds to move files from one category to another...

If these are keywords and you have hundreds of them, use the Metadata Mechanic to replace "Clothes" with "Clothing" in the keywords of the affected files. This should also do the trick just fine.
You could also use a metadata template for the same trick.
Try with some files first to check if it does what you want.

[Darius1968]

Your suggestions of the Metadata Mechanic and Metadata Templates, I have already (with some success) used on keywords.  But, how do I use these on IMatch categories?  (I cannot select the variable {File.Categories.Direct}, in Metadata Mechanic.) 

[Mario]

You cannot use them in regular categories. I assumed you were still working with @Keywords.
So, no shortcut. Just cut & paste or drag & drop.