If you have separate ticket AMS-DUS then DUS-AMS-XXX, I think you will still need to do airside->landside->CI->security->airside.

You will probably be in a big rush; especially if your flight is delayed, the check-in may still close 45 minutes before departure, that will be super tight...

You can always skip your last leg when you have no checked bags, simply tell them in the transfer counter if you want to leave and inform them you're going to "no-show" for the last segment.