Create an action of the type "Format value" for the target field, e.g. CONTENTGROUP
Format string: %popularimeter%
(I assume that the rating are stored in this field - see also the extended tags dialogue for the name of the field where you stored the rating. This could be RATING MM, RATING WMP, RATING WINAMP or POPULARIMETER.)
You can call this action any time you like and for as many files as you like. It does not run automatically, though.
Thanks for the quick reply ohrenkino. Your suggestion helped me figure out what I needed to do to get the output I wanted. For others that may see this post here's the notes:
Overview: Moving NI Trakto library to Serato. Track Rating tags are not supported in Serato. Grouping is. Objective: Copy Track Ratings tag to Grouping tag Key notes: Traktor (also MusicBee and others) store the Track Rating tag in the %rating wmp% tag. Serato stores the Grouping column in the %contentgroup% tag
Details: As ohrentkino noted - Create an Action to Format Value "CONTENTGROUP": %rating wmp%