I have a question in a similar vein....Can the base classes of a core set (not the end of the campaign ones) be mix and matched? I.e. could I run rise of the runelords with 2 character "sheets" from skulls and shackles? Just got this game today, played through a little bit and loved it!
If the character is completely out of his element (eg. a gunslinger in an adventure with no guns) grab the character's Class Deck. At the end of a scenario (or whenever you think it's appropriate, since the character may be at a disadvantage to others who will benefit from what they pick up during the scenario) you swap out (you could do this randomly or by choice) one card in your character's deck for a card from the Class Deck of equal rank (eg. a Basic card for a Basic card). Source: Organized Play rules.