For example you decided detach completely taxonomy Product Material from posts or any custom post type. Do next steps:
- Using the functionality of the tab 'Filters' make filtering of the posts by type if you need it
- If you need to change only some posts you can select them using checkboxes in the Posts Editor or skip this step. Also you should know that you can do this operation without any filtering using posts selection by checkboxes only.
- Go to tab 'Bulk Edit' and enable there in section taxonomies attribute 'Product Material'
- Do not select any terms in the drop-down for the 'materials' there but select behavior in the near drop-down: 'replace'
- Click on 'Do Bulk Edit' and wait until operation is finished
- If you want you can rollback changes in the tab History