Paste IMatch Categories (Merge, Not Overwrite)

[Darius1968]

I have one image file that has just one regular category assigned.  And, I wish for this file to get four new categories from another file, for a total of five categories. 

So, I did a Copy (Ctrl+C) on the source file, and then, a Paste Attributes (Ctrl+Shift+V) on the destination file, with only "Categories" checked. 
The result was that the original one-category-assignment got overwritten with the four new categories.  But, I don't want to overwrite; I want to merge. 
So, what to do? 

[Mario]

This is how this works. It copies the categories, replacing what's in the target. No merge.