Wanna Be Vampire and class changing

[Rylanthegiant]

My friends and I had a small dispute about the rules. My friend needed help with a wanna be vampire and was not a cleric so he was trying to fight and was going to ask for help. He then told one of the players not in combat to switch classes, then join him so as to just have the vampire run away. Is this legal? Do the rules of changing classes "in combat" apply to everyone, fighting or otherwise?

Also, in the next game, my friend was level 9 and drew the wanna be vampire and was a cleric. We argued it simply ran away but he disagreed and said he had to utter the phrase "booga booga" as printed on the card. Is the fleeing optional in this case? Can he fight it if he so chooses?