No. Of course they can improve. There's many examples of this over the years. It's quite typical that new users don't really care too much, and then change their mind as the forum grows on them, almost becoming a sort of second home to a lot of users here.

People in general deserve second chances. People develop over time, and typically learn from their mistakes. However, this varies from user to user, and I imagine most signature campaign managers would take this case by case instead of automatically ruling out users based on their past posting habits.