I think it's probably easier to just make up extra role cards, since you have some extra basic deck cards. The problem with introducing new roles would be that they'd be a lot less useful against some of the existing obstacles that require particular damage colors, and the existing roles would be useless against obstacles requiring new colors of damage. You could probably invent new roles with different combinations of existing starting cards, though. Like an adept (maybe 3 black, 2 blue, 1 red, 1 green?) or a rigger (maybe 3 green, 2 black, 1 red, 1 blue?), or just put in an extra one of the basic roles. The basic box comes with 2 extra starting cards of each color, and the expansion pack comes with an extra starting card of each color, so you could manage something for a 5th player just from the basic box if it were balanced 2-2-2-1. You'd need more cards for a 6th unless you were at the karma level that allowed substitutions All it really determines is the starting deck, and the rest is determined by what cards you buy.