We've played this variant only with both the Virulent Strain and Mutation expansions in effect.

1. Remove the New Assignment card and place it face up. Any time during the course of the game, this card is available for any player to use to switch Roles with any Role left in the Role deck as long as all players agree. Discard after use.

2. Deal two Role cards to each player face up. Each player decides which one of their two cards to keep, generally in discussion and coordination with the other players, and then places the other card back into the Role deck.