you can't have two niw at same time

You can 1). transfer or 2). withdraw first one and file a new one.

If you file two niw (or any other I140 at same category), both may be denied. Or worse, if one is approved, and then the other is denied later, the overall result will be denied.

In the past, there might be the case one center didn't know what other centers were doing; someone may be able to file multiple cases without being detected. Now the loophole is closing with the improved network. You may decide to take a risk to see how it goes. If so, report back and let us know the result.