Why do you think morality doesn't change? The basis of morality is what's good for society in the long run. If people stay with their old morality, they will simply die.
However, this is not to say that there should be no morality. There should be a new morality that lets people survive as best as they can for as long as they can. (How does taking food from other people to give to a dying Duck help people survive? How does staying at the pharmacy looking for pills long enough for the zombies to attack and kill someone help the group survive? How does taking care of children or injured help the group survive?)
I think the morals I suggested are good ones for The Walking Dead. When injured, moral people should want to be killed as quickly as possible, with wasting as few resources as possible. Taking up resources kills other people, which is wrong. Injured people who are truly moral should even volunteer as bait to distract zombies, because it helps others survive. It is selfish and wrong to waste a bullet to die without saving anyone else (unless they are too weak, like with Duck). When items are unattended, moral people should take them and be grateful that those items will help them survive longer.
However, it remains immoral to kill people for no reason or to take stuff that is attended. That hurts the survival of other people.
To answer my own question, honesty is probably more moral than lies. In episode 3, people died because Ben kept secrets and gave away stuff.
For the farm in episode 2, it was immoral because the farmers lied to people, which resulted in deaths. I think it would have been moral if the farm had offered to let the group stay if they agreed to become cannibals and eat whoever became weak or sick. This is why, as Lee, I had no problem killing everyone on the farm. Those farmers were an immoral threat to the survival of other people.
Again, I'm not talking about real world morality. I'm trying to explore what morality means in The Walking Dead, where everyone is guaranteed to die, and the only question is how long they can survive.