Change the badass stats to what you want, then distribute a badass point the regular way. That'll save them.
Maybe. I constantly have the game set to think it's got 4 players, but I never noticed a difference on the slot machines. And I use them alot.
Maybe the game's smart enough now to notice the difference between 4 logical players and 2 actual players. Mind you, the difficulty definitely skyrockets when played with 4 logical players. But I havn't seen a substantial increase in rare loot drops, nor as mentioned a better slot machine outcome.