Multiple Persons In Image

[Darius1968]

So, I have a set of 51 files, all having one or more vales for the
{File.MD.XMP::iptcExt\PersonInImage\PersonInImage\0} tag (; used as the separator).  I now want to add another entry for all 51 of these files on the fly, but I also don't want to overwrite the existing values, which the metadata panel will do, if I mess with the (MULTIPLE VALUES) setting.  So, what are my options to achieve my goal?  Thanks. 

[Mario]

This tag is added/modified by IMatch when you assign persons to faces in the image. You usually never manipulate this directly.

but I also don't want to overwrite the existing values, which the metadata panel will do,

When you select multiple images, the MD panel merges the tag contents of these images.
If the images have different tag values, you'll see (Multiple Values). When you change the tag content, the Metadata Panel writes the new content to all selected files.

You cannot select multiple images with probably 50 different persons and then somehow append one person to each file in the Metadata Panel. This is probably better done using a Metadata Template or for add-hoc ops, the Metadata Mechanic.

What did you try to so far?