It seems to me that many people in fact do not know this, but you do not have to replay the campaign to choose the other mission that you did not pick. Such as the Tosh and Nova missions. 1. Log in to Battle.Net 2. Click on Single Player 3. Continue the campaign 4. Go to the bridge and click on "Mission Archives". You can choose the other mission even if your still in progress with the campaign, you don't have to wait until you finish it, or restart.
This should be in the spoilers section. As people who have not played this would not know that the choosing missions even exist. I'm just lucky I have already done the ones you speak of. I want to play the campaign at least once through spoiler free.
