It probably would be best analyzing more then 1 team, but consider Green Bays switch from 4-3 (2008) to 3-4 (2009), you can turn a defense around pretty quick. That being said, Green Bay does have a lot of "names" on defense and Dom Capers.
2008: total yards(20th), scoring (23rd), rush yds (26)
2009: total yards (2nd), scoring (7th), rush yds (1st)