If I understood correctly, you can use an advanced search in you field modifier, for example if you are using a table chart with dimension MovieID and expression

=Avg(Rating)

, you can add a filter to this chart using a set expression like

=Avg( {<MovieID = {"=Count(Rating)>5"}>} Rating)

Only movies with more than 5 ratings will be shown.

You can also create a filter pane with a calculated field dimension to filter on the movie IDs, applying the filter to all charts:

=Aggr( If (Count({<MovieID=>} Rating)>5,'more than 5 ratings','less than 5 ratings'),MovieID)