indeed I succeeded.
With your help it was quite easy to read the arousal and valence out of the mood and to write the values in the grouping field.
But then I discovered, that I would not be able to sort my tracks based on the arousal because the lowest arousal values range from -90 to 90 and the grouping field is of text type and therefore iTunes and beatunes would sort it in the wrong way.
So I rewrote the code, so it would write -90 of arousal to a00 and +90 of arousal to a20. Same with valence (v00 to v20).
I am sure you can write the code much better (probably extracting the functionality to transfer the mood values in a seperate function) - but it works for me.
Additional information on how I get my dj-tool Traktor DJ to display the arousal and valence values:
In the tool mp3tag I have written an "action" to copy the grouping tag to the label tag - something like:
format tag field "PUBLISHER": %contentgroup%
So now I am finally able to sort my tracks in my dj-tool according to the arousal of the tracks. This is a big advantage for me.