Will importing login items from LastPass change login items already in 1Password?

@james1964 All imports generate new items. No existing items will be modified, over-written or deleted by the import. The issue is that you will have duplicate items which may be difficult to find as they have slightly different names and/or URLs.
The groups in LastPass will become tags in 1Password. So, if you have a lot of existing items, you may want to tag them in a way that makes it easier to sort items and identify duplicates. Tasks like this are generally more easily performed in the desktop apps.