Prevent automatic asset number allocation

Are you able to prevent WHD from automatically assigning  asset numbers on import? When I asked the tech support guys they said it can't be done because the asset number is the sync key or something but this can't be true since you can manually change this asset number by going to the record, further to this I added a Discovery Sync ID and tried using this o sync but still not working.

Frankly I'm surprised nobody else has asked about this !