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There is an option to update metadata and linked assets through a csv. It is similar to what exists currently for textbooks. The functionality is detailed in this page: Create/Download/Update Collection Hierarchy using a CSV
Review comments
Reviewer has an option of providing comments (as a textbox) when requesting changes from the creator. When the creator opens the collection that is sent back for corrections, there is a comments icon in the editor (as in the current editor). Clicking that opens a textbox showing the latest comments from the reviewer.