When reading, list is a reference to the original list, and list[:] shallow-copies the list. When assigning, list (re)binds the name and list[:] slice-assigns, replacing what was previously in the list. Also, don't use list as a name since it shadows the built-in.
Zotero is, at the most basic level, a reference manager. It is designed to store, manage, and cite bibliographic references, such as books and articles. In Zotero, each of these references constitutes an item. More broadly, Zotero is a powerful tool for collecting and organizing research information and sources.
For Word .docx documents, you can use Reference Extractor. Note that to continue using the same document, you'll want to replace all instances of the original citation with the new item from your library, being sure to select from the library section of the citation dialog's search results rather than the Cited section.
When using Zotero — or any other reference manager — for citing, you should always check items for accuracy after saving them to your library. Zotero will accurately import metadata supplied by most bibliographic databases, library catalogs, publisher sites, and webpages.
The Export preferences pane is used to choose a default citation style or bibliographic data format and configure other settings for copying data from Zotero. For information on adding and removing citation styles from Zotero, see Citation Styles and the Cite pane in Zotero preferences.
By using a : colon in the list index, you are asking for a slice, which is always another list. In Python you can assign values to both an individual item in a list, and to a slice of the list.