You can classify all comments of a collected post at the same time.
It's a piece of cake.
Scup collected this post:
Notice that 21 comments were collected from this post.
I marked the post with the tag News.
When I did so, Scup displayed an orange box in the upper corner of the item.... CLICK THIS BOX.
A screen opens up that notifies the existence of more items that can be tagged/classified.
This resource is available for up to 1,000 items and does not apply tags to replies or comments on replies (answers to replies).