I've found a bug in DOFF Assignment rewards. Let's say you do Experimental Assault weapon upgrades. You finish the mission and it's a success. It offers you a blue blast type phaser. Well that's a bit boring. Click to any other assignment in the list and then click back. The reward has magically changed! Keep clicking until you find what you want. However there is one downside to this. You won't actually get rewarded anything you see.