Let's find out how to add a new list of contacts to your existing contacts list on Mac.
I'm in a Mac-users group, and I'd like to add a file with my fellow members' contact info to my existing contacts book. All the info has been exported as an archive, but when I try to import it, I get a warning stating that all existing contacts will be erased. How do I add the contacts without wiping out the old ones?
Instead of exporting the contacts as an archive, select all the contacts and click File > Export... > Export vCard. This creates a single VCF file with all the contacts in it. Import this to Contacts and the imported names are added to the existing list.
If you don't have access to the original contacts list that created the exported archive, create a new user account and log in to that. Now import the archive to a clean Contacts list, select all of them and re-export it to create the vCard as before. Save this in the Public\Drop Box folder of your main account, log in to that account and import the file to the original Contacts list.