How would I place BoS paladins at rivet city? Should I just copy to outcast patrol packages and put it into the BoS?

You should be able to load a BoS Paladin NPC at rivet city, unless you want the Named paladins to walk there? (that would be a long, long way). They would most certainly be killed by respawning mutants eventually.

But just placing generic paladins there as NPCs shouldn't be a problem.

Miax