Writing xmp data to png file

[tzvika]

Probably that question was answered few times before, but didn't find it.
I want to use ExitTool as command line tool for adding xmp data to exist png file, without override exists metadata, and use 1 command for the whole structure, which might be something like this :
<rdf:Description rdf:about=""
            xmlns:myTag="http://www.myapp.com/1.0/">
         <myTag:Folio>data</myTag:Folio>
         <myTag:id>id</myTag:id>
....... some more myTags
</rdf:Description>

Is it possible?

Thanks for any help

[Phil Harvey]

If you don't want to overwrite existing XMP then the tags must be individually writable by ExifTool.  If you have custom tags you must create corresponding ExifTool user-defined tags to be able to write them.  Then, a command like this will do what you want:

exiftool -tagsfromfile YOUR_XMP_FILE -all:all EXISTING_PNG_FILE

- Phil