You are free to commit crimes anywhere in the City. However, performing crimes against civilian infrastructure or within the public areas of the City requires at least 4+ CPs online. If you are unsure of the current CP count, type in the command /checkcrime. Slums and Sewers do not count as part of the City.
If you are desiring to take the initiative with a rebel group and desiring to attack the Combine DIRECTLY with armed assaults, bombings etc on their territory, 5+ CPs online are required. This is to SIMULATE a proper response force capability, should it happen. You can always ASK to see if the count is above 5 to enact insurgency against the regime itself.