Yes and Yes, but you will be creating more work for yourself. 
You can change anything about a knowledge pack item except for the 1) question/topic or 2) answer/article.  When updating the knowledge pack items, we do not touch anything but these two fields, leaving everything else (including the category) in tact.  When adding new knowledge pack items, we will add the new knowledge pack items using the category for the knowledge pack item as we know it.  It is then up to you to move these new knowledge pack items out of draft and into the desired categories.  If you have not moved the knowledge pack items to different categories, you only need to move the desired knowledge pack items out of draft to be viewable.