Well .. database names, user names, passwords and privileges are in the MySQL database itself (as you probably would know).
I don't see why you'll need to be able to log on as every user with sqlyog. You can create ONE user and give that user any set of privileges that you need to all bases (if they are on the same server). There is also the server's ROOT user available.
But the answer to your question: importing from a text-file: No!