Yes, you can do this, by following these steps:
1. Index your first book normally and in Step3 click Export words button found in the Tools bar.
2. By clicking the Export words button a window will appear which will allow you to export all or some of the words in the table of results to an external file. You can also determine what data to export, i.e: word title, pages, count, type.
3. You can export your book words to a *.txt file or a *.pdfig file. We recommend using the *.pdfig file.
4. Create your new index project and when you reach Step3, click Import words button found in the Tools bar.
5. The Import words button will allow you to import your first project exported words file to the current Index.
6. When you import the words file, you will see your first project words are now merged with the current Index as required.
Note: If the 2 Index projects have duplicate words, then the duplicated words will not be overwritten by the imported words, but the duplicated words will be imported as new words. To remove the duplicated words you can click the Merge duplicates button found in the Tools bar.