Because there's no name under the imperial/rebel officer command cards, can I take those cards if I don't have an officer in my list?

You can take those cards with any Commander.

Do they replace that commanders commander specific cards?

1 minute ago, lologrelol said:

Do they replace that commanders commander specific cards?

You have to have two cards of pip values 1-3 and the 4 pip Standby.

That can be any combination of cards you like, but only pictured commanders can play their own order card.

The ones that come in the Personnel packs are generics for each faction side, anyone can use them.

If you wanted to you could use the base set generic cards and the personnel cards...although that seems pointless if you brought a unique commander.