In YA-Cas you can enter both the household name and, per Sim individually, a surname.

Is there a mod that makes this available in normal CAS?

Don't think so. It works that way in Uni CAS because the game presumes you want to create households of unrelated dormies. In the main game it assumes you want families.

You can reproduce the same effect - everyone having a different surname - by creating each one as an individual and moving them into the same lot one by one from the Sim bin. The household will take the name of the first Sim moved in, but they'll all have their individual surnames within it. Or you can change their surnames in game with something like Sim Blender or Sim Manipulator. Think you can change the household name by editing it from neighbourhood view, but I don't have access to my game just now and haven't renamed households for a while so can't guarantee that's not just my imagination.

Following up on the above, you can also use SimPE as an alternative and edit Sim names and even household names. You could have a household called "Frat Guys" but none of the Sims in the household have that surname.

I know there are other ways (I use them myself), but both the household name and the surname would be so great to have in CAS.