Unless I am not understanding your intent....
Index entries are linked to existing topics. If this is a new project, you can import existing topics and the index entries will be imported as well. Similarly, if you are importing a Word document, you have the option to import the index entries.
Importing the index entries without the topics makes little sense because the keywords have to be included (explicitely in the text) or separately as a keyword, linked to the topic. Without the topic, the index entry has no "home".
Thanks, Peter. This is great. It achieved what I needed to do.
Thanks, Paula. I had separate projects with identical topics. I had made a lot of extensive changes to mobile.css for Multiscreen HTML5 output in one of the projects, but that one didn't have index tags. (I had copied a version of the original project before I added index entries and finally had the mobile.css the way I wanted it. However, if I copied that mobile.css to the indexed project, a lot of things went wrong.) It was just easier for me to copy the index to the project with the "good" mobile.css. Thanks.