Bulk edit structure on owned cabinets, not library items
Bulk structure edit only works on owned cabinets and wardrobes, so copy a library item into your own folder before changing its construction.
Bulk editing of cabinet construction/structure applies only to owned cabinets and wardrobes.
To edit such items, make a copy of the item, paste it in the same folder, rename it, delete the original, and then change the construction of the copy.