But what if i want to allow a normal, anonymous, not-logged-in user to access my Perl wiki too (which is the same executable)? Is that possible?

It is certainly possible to do something like giving write access to logged-in users while allowing anonymous users only read access. Try

  <Files "login.cgi">
    <Limit GET>
      require valid-user
    </Limit>
  </Files>
[download]

The login CGI merely redirects back to the referrer, since Apache will have done the grunt work of checking passwords. Then, in your Wiki scripts, require a logged-in user before allowing write operations.