Looking through forum I did find an answer: is there a way to assign a co-author to multiple pages at once? Like chekboxing pages and then Bulk action --> Assign a co-author(s).
Asking since we run a site with a large number of static pages which are editable by different group mambers, and often I need to add one or more co-authors to 10 pages or more, that are owned by one particular group. Right now I must go through all 10 pages one by one and add co-author(s) to each. Is there more sophisticated way?