Import bib file into groups, not creating duplicates

I have a .bib file I want to import into my main library. This bib file contains some existing entries and some new entries.
I also want to import the file into a group, adding all existing items to the group.
I used 'C:\Program Files\JabRef\runtime\bin\JabRef.bat' -importToOpen scopus.bib for triggering the import.

However, I can not figure out how to do that:
If I click on the “possible duplicate of existing entry. click to resolve” button and select “keep merged entry only”, I still create a duplicate on import. I’m not sure if the help from here: Find duplicates - JabRef applies to the import as well? Because it says when clicking merge, “Both previous entries are removed.” - which can not apply to importing, because there is simply only one entry existing in the library, right?

The usecase for this is the following: I did some search on scopus and downloaded all articles as bib. I then want to create a group containing the search results. If the article is already in my library, I would like to add it to the group (potentially also adding additional fields, found in the import). If it is new, I would like to add it to the library and the group.

A workaround (although, I did not tested it) would probably be to importing regardless of creating duplicates and then merging the entries again.