According to what I heard at the time, Worf's forehead changed because someone broke into Michael Westmore's workshop and stole the mold.
Although I could swear there was a supporting Klingon crewmember in "A Matter of Honor" who had Worf's season 1 forehead.
Spock lost his mind in "Operation Annihilate" and attacked everyone on the bridge. He was screaming. He tried to take the ship down.