Limiting drilldown based on n value

IF the n<5 relates to a column, you could simply filter it out within the Transform Data Section (M Code).  If you need the aggregate data for measures, but you simply do not want to drill into the details, an option would be Duplicate the data within M Code and then filter this copied table.  Then you create measures on your original table, and then drill into the duplicate table that is filtered in the background.