(Here is an optional rule from my old Ground Zero game that may help differentiate PCs in Tempora Mutantur. It’s not big enough for it’s own one-page rulesheet, so I’m posting it here.)
Quirks are aspects of a character’s personality, background, or physique that makes him better at some activities and worse at others. Quirks are not mutations, but in many ways they resemble both perks and flaws. Each quirk provides some benefit, but carries a corresponding drawback. In addition to their game effects, quirks suggest personality characteristics that might lead to interesting roleplaying opportunities.
If the player wishes for his PC to possess a quirk, he may roll on the following table (click to embiggen):
Quirks are typically determined during PC creation, and there is a maximum of 1 quirk per character. If the referee allows it, players may add quirks to experienced characters. A player may be allowed to assign a quirk to his character after he has roleplayed the PC in a manner consistent with the quirk in question, or after a traumatic or life-changing experience.